In this argument, it is concluded that predation by coyotes was the cause of the rabbit decline in Nova Scotia between 2000 and 2010. However, the evidence for this conclusion is quite weak. While disease and undernourishment are eliminated as causes of the decline, it is entirely possible that the decline was caused by a different predator. While deer, the preferred prey for coyotes, did decline in this period, this does not prove that coyotes were responsible for the rabbit decline. Therefore, the correct answer should be something that gives additional evidence supporting coyote predation as the cause of the decline. For "Despite a substantial decline in the deer population between 2000 and 2010, there were still enough deer to support the coyote population in the region.", if this were true, then it would suggest that coyotes were NOT responsible for the rabbit decline as they would still be able to feed off the deer, their preferred prey. For "It is difficult for most wildlife biologists to properly assess whether the decline of an animal population is caused by disease or undernourishment.", this answer choice addresses the possibility that wildlife biologists might have missed some cause relating to disease or malnourishment. However, if this is true and the decline was indeed caused by one of these things, that would weaken not strengthen the conclusion.

For "Between 2000 and 2010, the rabbit population on several islands off the coast that are inaccessible to coyotes did not decline.", this gives additional evidence supporting the conclusion. If there was a place that coyotes were not present over that period and in that place the rabbit population did not decline, this helps build the case that indeed coyotes were the cause. Remember: the given argument provides no evidence that the cause was coyote predation; the only evidence is "it wasn't one of these two things that aren't coyote predation." So any evidence that ties coyote presence closer to rabbit decline is helpful. For "Coyotes are known to eat mice and other vermin, ground birds, insects, and even fish.", whatever else coyotes might eat is not relevant, as you don’t know what happened to those populations and how that would affect coyote predation of rabbits. For "Since 2010, the rabbit population has recovered well while the deer population has declined even further." whatever happened since 2010 is not important, as this argument is only concerned with explaining a decline during the particular period from 2000 to 2010. The correct answer is "Between 2000 and 2010, the rabbit population on several islands off the coast that are inaccessible to coyotes did not decline.".

Whenever you are asked for an answer that "most logically completes" an argument, you can determine what type of question you're dealing with by looking immediately before the blank that the answer will fill in. Here that blank is preceded by "since," so you're looking for a reason, and before that it's "these processes do not prevent harm from some drug enantiomers." So you're looking to provide a reason that these processes don't prevent harm - you're looking to strengthen that idea.

In any strengthen/weaken problem it is extremely helpful to notice the gap in logic between the premises and conclusion, and here the "extra" information just before the conclusion gives you great insight into that. Notice the modifier "during the drug creation process" - that gives a good deal of specificity as to where the prevention of harm takes place. It limits the prevention of enantiomers to that narrow scope "during the drug creation process," leaving enantiomers to emerge during any other time period (during transport of the drugs, the drugs' interaction with their containers, when taken in combination with other drugs or foods, etc.). If you notice that, you can scan the answer choices looking for some other timeframe when these enantiomers emerge.

Choice "the metabolism of some drugs within the body can create harmful enantiomers regardless of whether the drug itself contains those enantiomers." gives you exactly such a situation where this could happen. If the metabolism of the drugs leads to the creation of the harmful enantiomers, then there is no way that changes in the production process can mitigate the effects of harmful enantiomers. Choice "the metabolism of some drugs within the body can create harmful enantiomers regardless of whether the drug itself contains those enantiomers." exploits that gap in logic and is correct.

Among the other answers, choice "not all drug enantiomers are harmful and some can even be helpful in fighting certain diseases." can be eliminated because the argument is about exposure to harmful enantiomers, not whether all enantiomers are necessarily bad. Choice "many enantiomers only cause minor side effects rather than major health problems when ingested." can be eliminated because the argument is about limiting consumer exposure to all harmful enantiomers regardless of severity. Choice "the creation of harmful enantiomers are not the only side effect that drug manufacturers should seek to reduce." can be eliminated because the argument is only about enantiomers, not other side effects, and choice "enantiomers are difficult to detect and cannot be pinpointed as the cause of some health problems." can be eliminated because it does not deal with whether it is possible to limit consumer exposure to harmful enantiomers.

As you assess the argument, you should notice that there is very little direct evidence given for the conclusion that tusks without imperfections are almost certainly counterfeits. The premises only state that there is demand for tusks and that the counterfeiting of tusks is now an industry, but the conclusion is specific to one particular feature of tusks - if they're free from imperfection, they're counterfeit - without any evidence given for that. So your goal in the answer choices should be to find either a link between imperfections and authenticity or a link between perfect tusks and counterfeiting.

Choice C provides that first link: if real elephant tusks are often imperfect because of the way that elephants use their tusks, then it stands to reason that perfect tusks likely aren't authentic. Choice "Elephants regularly use their tusks to scrape bark from trees, a process that leads to the frequent chipping and breaking of tusks." is correct.

Among the incorrect answer choices, choice "Counterfeit ivory is often damaged during shipping due to the fragile material necessary to make the product cost-effective." actually weakens the argument by giving a reason why counterfeit tusks would have imperfections. And choices "Many ivory purchasers are aware of the counterfeit market and are as happy with fake ivory as they would be with real ivory.", "Some governments in developing economies have encouraged the counterfeit ivory market as a way to satisfy demand without harming animals to increase the supply.", and "The process of counterfeiting ivory has become so sophisticated that it is difficult for most people to tell the difference between authentic and counterfeit tusks." miss the point of the conclusion entirely - none of them deals with the link between perfect tusks and counterfeit tusks.

Recognize, also, an important lesson here: extra words (modifiers, adjectives, etc.) matter in conclusions! The most popular incorrect answer choice, "The process of counterfeiting ivory has become so sophisticated that it is difficult for most people to tell the difference between authentic and counterfeit tusks.", gives a reason that buyers should be careful in general. But the conclusion is that buyers should beware specifically of those tusks that have no imperfections. That modifying phrase "that have no imperfections" is crucial to your understanding of the argument.

With Strengthen/Weaken problems, it is important to read adjectives, modifiers, and anything else "additional" that specifies the conclusion, as that is often where the gap in logic lies. Here the conclusion is "clearly, the students are misinformed in their complaint," which should encourage you to look at the specificity of that complaint. Their complaint is not about "class sizes" in general, but more specifically "the size of classes taught by the most popular professors."

This is critical, as it sets up the gap: the statistic given is about the general student-to-teacher ratio, not the ratio for those specific classes taught by the most popular professor. So as you approach the answer choices, you're looking to exploit that gap: how could the overall ratio have become lower, while the ratio for the classes in question have gotten higher.

Choice "Many of the most popular tenured professors commonly teach courses that have ten times the number of students enrolled in an average course." exploits that gap perfectly: if the classes of the most popular professors have 10 times the typical number of students, then the general ratio doesn't apply to the specific complaint. Therefore, choice "Many of the most popular tenured professors commonly teach courses that have ten times the number of students enrolled in an average course."is correct.

Among the other answer choices, choice "Most of the faculty members at the university are part-time instructors or teaching assistants and not full-time, tenure-track professors." is a good distracter choice. It would seem that if most of the faculty members are not full-time professors that the professors would have larger classes, yet this requires an assumption that choice "Many of the most popular tenured professors commonly teach courses that have ten times the number of students enrolled in an average course." does not. With choice "Most of the faculty members at the university are part-time instructors or teaching assistants and not full-time, tenure-track professors." it is still possible that all courses have even numbers of students and those courses taught by full professors have only 14 students. Choices "Some other universities in the state have lower faculty-to-student ratios." and "The average class size at the university varies from department to department." do not bear directly on the question as to whether the size of the courses of popular professors is increasing. Even if true, Choice "None of the students who complained is willing to pay increased tuition in order to have smaller classes." does not indicate whether the students are misinformed in their claims about class size.

On this Strengthen question, note the potentially paradoxical logic the fire departments use. Their concern is safety (an important clue the testmakers leave in the sentence that outlines the departments' actions), so why would they choose not to extinguish small fires?

Choice "Only some small brush fires expand to become large, catastrophic fires." is inconsistent with the idea of safety. Even "only some" small fires turn into catastrophic fires, failing to extinguish them risks or sacrifices at least some safety. And that is certainly not a reason to actively choose not to extinguish them in the name of safety.

Choice "Most fire departments would be unable to extinguish every small brush fire without having to hire additional staff." also falls victim to the notion of safety. If the fire departments had cited cost as their reason, then "Most fire departments would be unable to extinguish every small brush fire without having to hire additional staff." totally works - hiring more firefighters to fight these small fires would certainly come at a cost. But if their cited concern is safety, the reason that "we would have to hire more people and spend more money" is not consistent with their stated goals/priorities.

Choice "There is no means other than fire for clearing dry brush and debris in wildfire-prone areas." is correct. If letting the small fires burn is the only known way to eliminate the brush that could fuel a larger fire, then choosing to not extinguish the fire works with the idea of safety - that decision is made to help prevent larger fires from having sufficient fuel to be catastrophic.

Choice "The most common causes of small brush fires are carelessly-discarded cigarette butts and poorly-extinguished campfires, each of which is easily preventable through fire education." is incorrect in large part because of its timeline. The departments are choosing not to extinguish fires that are already burning, so relying on education to prevent new fires from starting isn't a valid reason - that solution will do nothing to help the existing fires.

And choice "Small brush fires enrich the soil beneath them, leading to fertile land for agriculture and natural beauty." simply misses the mark of safety - sure, the fires might leave a beautiful, productive landscape but if safety is a cost of that then the fire departments are violating their stated reason for the choice not to extinguish the fire.

With Inference questions, the correct answer has to fit the "must be true" standard, meaning that it has to be proven based on the passage; incorrect answers "could be true" but are not necessarily true based only on the information in the passage.

Here choice "The kitchen staff at Barry’s sometimes prepares multiple dishes on the same grill." fits that standard largely because of the phrase "under normal circumstances" at the end of the stimulus. If the prohibition on preparing multiple dishes on the same grill is different from "under normal circumstances," then it must be true that "sometimes" (note: "sometimes" is a very low bar to clear for proof) multiple dishes are prepared on the same grill. Choice "The kitchen staff at Barry’s sometimes prepares multiple dishes on the same grill." is therefore correct.

In contrast, notice the strong language within choice "Barry’s will not make special kitchen accommodations for diners who do not make a reservation.", that the restaurant categorically will not make kitchen accommodations (of any type) if a diner does not make a reservation. From the stimulus you know of one particular accommodation that will be made under a reservation, but you cannot conclude that there are no other possible accommodations, or that the restaurant wouldn't try to make that accommodation if someone were to arrive without a reservation.

Choice "Not all restaurants follow food allergy precautions to avoid cross-contamination between multiple dishes." could possibly be true ("not all" is another low bar of proof) but as this stimulus only tells you about one particular accommodation that one particular restaurant makes, you just do not have evidence to support this. (Note that while "not all" is a low bar, "food allergy precautions" is fairly broad: if every restaurant, for example, takes one small precaution like washing its dishes at high heat, that would be enough to rule out "Not all restaurants follow food allergy precautions to avoid cross-contamination between multiple dishes.".)

Choice "Limiting cross-contamination from multiple dishes on the same grill is the most effective way to avoid issues for diners with food allergies." is a classic example of an Inference answer choice simply going too far, using "the most effective" when you simply do not have information to rank different precautions.

And choice "Diners with food allergies are generally willing to be patient with longer wait times in order to avoid cross-contamination between dishes." is another example of a choice that might well be true, but does not have any proof in the stimulus.

This inference problem forces you to do some math to determine which answer must be true. You know from the given information that some preferences were different between the survey and the taste test (dark chocolate went from 27% to 60%, from the lowest value to the highest, so some people must have changed their preferences from either milk or white chocolate), but each answer choice will require some analysis to determine whether it "could be true" (incorrect answer) or "must be true" (correct).

Choice "The survey participants were generally inaccurate regarding their chocolate preferences." is the qualitative answer and certainly could be true, but isn't necessarily. What if this company simply has lousy white and milk chocolate, but very good dark chocolate? The respondents could have been very accurate in relaying their general preferences, but those preferences just didn't hold in this particular case. So choice "The survey participants were generally inaccurate regarding their chocolate preferences." is incorrect.

Choice "Some people who stated a preference for white chocolate in the survey preferred dark chocolate in the taste test." is more quantitative. It certainly could be true but doesn't have to be. You know that dark chocolate went from 27% to 60%, so it picked up a net gain of 33%. This could be true if some of that gain came from white and some from milk. But since you do not have the taste test totals from white and milk you can play with different combinations. Suppose all who said dark in the survey said dark in the taste test, and then 33% defected from milk to dark. That would leave white unchanged and still give you 60% dark, just with 28% white and now 12% milk. So choice B is not necessarily true and is therefore incorrect.

Choice "Some people who preferred milk chocolate in the taste test had initially stated a preference for white chocolate in the survey." does not have to be true, either. You know that 33% of respondents switched to dark chocolate, but you do not know for certain that anyone switched between white and milk. As you will see with choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test."...

Choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test." must be true. You need a net gain of 33% moving from either white or milk to dark. And since only 28% preferred white chocolate, you can't get that 33% gain unless at the very least 5% of people changed from milk to dark.

Choice "Most participants expressed a different preference in the taste test than they had indicated in the survey.​" is incorrect because, again, the minimum change is 33%. All the statements could be true if everyone who liked dark in the survey stuck with dark in the taste test, and then 33% moved to dark from milk. That case satisfies all of the facts but leaves more than half of survey responses intact, thereby invalidating choice "Most participants expressed a different preference in the taste test than they had indicated in the survey.​". Choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test." is correct.

As with any inference question, your job here is to understand the information given and to choose an answer choice guaranteed by the text. You are told in this stimulus to this question that free trials are meant to increase sales of the full version of an online service by giving users who would not buy the service without trying it first a chance to experiment with it. Choice "The number of people who see the free trial as an acceptable replacement for buying the online service is not greater than the number of people who buy the online service because of their experience within the free trial." is the only answer choice that is guaranteed by the text. If the number of people who find that the free trial was a good substitute is bigger than the number of people who are incentivized to buy the full online service because of the free trial, then the ability to experiment before you try the full service would not only be meaningless, it would be counter to the reason that companies offer free trials.

Among the other answers, choice "Because the cost of offering a free trial can be high, companies are often resistant to offering free trials, especially free trials that offer all features included within the paid version of the online service." can be eliminated because there is no information about what makes companies more or less likely to offer free trials. Choice "In calculating the total number of an online service sold, free trials are generally included as zero-dollar sales rather than as a separate category." can be eliminated because there is no information given about the spread of companies’ free versus paid sales. Choice "The number of sales for a given online service is directly proportional to the number of visitors to the online service's website, a number that tends to increase if a free trial is offered." can be eliminated because there is no information about whether the two values are directly proportional at all. Choice "Online services that are easily adapted to free trial versions sell better than do online services that are not readily distributed as free trials." can be eliminated for similar reasons to choice "Because the cost of offering a free trial can be high, companies are often resistant to offering free trials, especially free trials that offer all features included within the paid version of the online service.". there is no information about the importance of the ease of creating a free trial.

The answer to this Inference problem is "Last year there were more copies of accounting software sold to non-accountants than in any previous year.". Remember - in an Inference question the correct answer must be true based on the premises, and "Last year there were more copies of accounting software sold to non-accountants than in any previous year." can be proven by the facts. You know that 1) the total number of copies of accounting software was its greatest ever and that 2) the percentage that non-accountants purchased was its greatest ever (the first time over 50%). So non-accountants purchased their greatest-ever share of the greatest-ever total, meaning that they must have purchased their greatest number of copies of accounting software ever.

Among the incorrect answer choices:

"Last year more accounting software was sold to corporations than in any previous year." very well might be true, but cannot be proven. What if the growth in accounting software was entirely due to non-accountants (perhaps this was the first-ever year that a program like TurboTax was available, and so the non-accountant software surged while several accountants went out of business and didn't purchase anything)?

"At least some non-accountants purchased the most-purchased copy of software last year." also could be true, but you certainly cannot prove it. What if the most-sold software was a must-buy for any corporation but had no appeal to individuals?

"More non-accountants purchased accounting software last year than in any previous year." is close, but note the precision in language there: all the premises are about the number of copies sold, whereas "More non-accountants purchased accounting software last year than in any previous year." draws a conclusion about the number of purchasers. What if the number of purchasers stayed the same or even decreased, but each purchaser bought multiple different copies (maybe TurboTax came with a "add on Quicken for a dollar" promotion and almost everyone who purchased one piece of software last year bought two this year?).

And "Last year fewer copies of accounting software were purchased by accountants than in the previous year." of course does not have to be true as there is no proof for it anywhere. You know that the highest total number of copies of accounting software was sold so it is difficult to believe that fewer were sold to non-accountants, and that's the only real evidence you have to get close to this conclusion.

With any Inference question, you must select the answer choice that must be true based on the information in the passage. Here, several choices might seem very likely, but the "must be true" standard is crucial for inferences.

Choice "Daily meditation sessions of an hour or longer can increase one's life expectancy." must be true. The premises state that "while longer sessions produce better results, all of the above benefits (including a longer life) are possible from daily-ten minute sessions." From that, you can infer that longer sessions (an hour vs. ten minutes) would at least produce the same benefits, if not better. Additionally, note the easier-to-prove word "can" in "can increase one's life expectancy." This is much easier to prove than "will" or "only," words you see in other answer choices.

Among the other choices, choice "Mediation is only effective if it is performed on a daily basis." goes too far with "only." While the last sentence suggests that daily sessions are effective, the previous sentence uses "regular meditation" (so not necessarily "daily"), and ultimately there is nothing to suggest that even infrequent sessions are completely ineffective.

Choice "People who meditate for ten minutes each day will live longer than those who meditate less frequently." goes too far with the prediction "will" - for one, the argument doesn't give enough information to compare daily ten-minute sessions with, say, five-days-per-week hour-long sessions. But just as damning is the word "will" - predictions are just very hard to prove. Can you conceive of a situation in which people who meditate for ten minutes each day live shorter (too much radiation from their Headspace app?)? If so, "will" is not necessarily true.

Choice "It is possible to achieve as much of a gain in life expectancy from ten minutes of meditation per day as from less frequent meditation sessions of an hour or longer." is wrong for similar reasons as "Mediation is only effective if it is performed on a daily basis." is wrong: the hard fact is that "regular" meditation is more important than the duration of each session, but "regular" does not necessarily mean "daily" so this comparison is impossible to make without further information. For the same reason, choice "Meditating less frequently than once per day will lead to less positive benefits than meditating daily." is also incorrect.