These two clauses contrast the sense of being an "option" or being "optional" to the word that is being required for the answer. In contrast to being "optional," something might be "necessary or a requirement. Therefore, "requirement" is the best answer of those given.

The parallel in this sentence is between being "horrible" and whatever it is that bribes do not necessarily do to politicians. To become horrible or morally bad is to become "corrupted." This is much better than "wealthy," as the sentence is not focusing directly on the wealth gained by some politicians; it is focused on the overall negative impact of political life on their character. This is best noted by "corrupted." Note also that the sentence does not necessarily say that they become tyrants—though political corruption might in fact lead to that.

The sentence is contrasting two temperaments, one that is timid and quiet and another that is the opposite. Clearly, Peter is assertive—to the point of questioning his elders. This does not, however, mean that he is "bratty." It may or may not mean that. Likewise, he might be "annoying" (pesky), but we do not know that necessarily. The best option is "forceful," which contrasts directly with the timidity of John.

For any sentence with a contrast like this one, you need to stay as close as possible to the direct meaning of the sentence. The first part of the sentence talks about the inside of the house and its "cleanness" (or tidiness). The contrast is with something that is untidy. All we are given to help us determine the opposite word is "inside." Therefore, the sentence must be contrasting the inside to the outside—not to the garage, nor even (if it were an option) to the lawn. It is to the "exterior," which means related to or visible on the outside of something.

"Palatable" means acceptable to the taste. The todler found the baked chicken inedible (unacceptable to the taste). The wrong answers are antonyms of "palatable," and while they may initially look correct, the "not" in the sentence tells us that we need to pick out a word that means "tasting good" or at least "acceptable to the taste," not "tasting bad."

Since the researcher disagrees with the skepticism of the scientists, she would be "optimistic" - hopeful and confident - about her experiments. None of the other answer choices make sense in the sentence's context: "indifferent" means apathetic, "doubtful" means skeptical, "expressive" means expressing emotion, and "poor" means lacking money.

In order to appear to have disappared, the rabbit must be hidden from sight under the table. The correct answer is "concealed," which is a synonym of "hidden." None of the other answer choices make sense in the sentence's context: "discovered," when used as an adjective, is an antonym of "concealed" and means revealed or exposed; "compiled" means put together; "drenched" means soaked; and "visible" is another antonym of "concealed," and means able to be seen.

Since George is pretending that he is able to perform calculations, we can assume that he must not actually be able to do such calculations. This is implied both by the fact that he is pretending as well as the use of "instead," which likewise indicates that there is a contrast occurring. In contrast to being able to do something, someone can be called "incompetent." This means that someone lacks a given "competency," or an ability or skill. This is the only option that expresses such a lack of ability.

This sentence is very direct regarding the contrast that it expresses. The word "superficial" means surface level or not complete or thorough. Already, you can see that the best contrast will be "thorough." Still, consider the wrong answers. "Cursory" means means not detailed—it is basically a synonym of "superficial." "Passing" likewise is a relative synonym of "superficial." While "scholarly" might appear to be detailed, this really expresses something else, namely the fact that something is being written for a specific type of audience (i.e. an academic audience). There can be superficial "scholarly" works. Finally, we do not know whether or not the review was "supportive," merely that it was not a superficial review. (Perhaps it was a thorough critique!)

The word "still" can be used to mean "nevertheless." In this sentence, this means that, in spite of the fact that the prediction had an improbable premise, it was still not completely improbable. The implication is that while improbable, it was still possible (not completely ruled out by the improbability that was mentioned). Without a doubt, it would not be fair to say that it was "certain."  The improbability mentioned above needs to be recognized. Likewise, the use of "still" indicates that it is not completely out of the question either.