Immaterial suggests that something is deemed unimportant or it lacks significance.  In this question, it calls upon the first definition of immaterial; the other definition of immaterial defines something as spiritual rather than physical.

Something that is "tentative" is unsure or uncertain. "Uncertain" is the best answer choice as it is a part of the definition of "tentative." "Certain" is an antonym of the word "tentative," and means sure or unavoidable; the other answer choices are unrelated.

To be cynical means to always see the bad side of things. Negative means to see things in a way that is the opposite of positive; badly. Thus, cynical and negative are synonyms. 

Something that is “absurd” is not normal, as well as ridiculous, so "silly" is the correct answer. If you are “proud,” it means you feel good about something you have done. "Clever" means quick-witted and smart. “Frightening” means scary or causing fear.

Something that is “blatant” is very obvious, very clear, and not confusing, so "obvious" is the correct answer. The word “fortunate” means lucky, something that is “terrific” is very good, something that is "muddled" is in disarray, and something that is "heavy" is weighty.

Something that is “natural” is something with which you are born, something unchanged by humans, or something allowed to remain as it normally is, so "untaught" is the best answer choice, as it is describes something you can do without being taught. As for the other answer choices, "abnormal” means not normal or weird; “wild” means untamed or living in nature; “chaotic” means not under control or not orderly; and “orderly” means organized or under control.

When something is "contrived," it is obviously artificial or obviously fake. So, "artificial," which means fake or man-made instead of natural, is the correct answer.

"Ludicrous" is an adjective that means "so foolish, unreasonable, or out of place as to be amusing; ridiculous." So, we need to pick out an answer choice that means something like "ridiculous." "Sensible" cannot be the correct answer, then, because "sensible" is an antonym of "ridiculous." "Preposterous," however, is an adjective that means "contrary to reason or common sense; utterly absurd or ridiculous," and because it is the answer choice that is closest in meaning to "ludicrous," "preposterous" is the correct answer.

The word "evident" is an adjective that means clear or obvious. For example, if a certain fact is evident, it is so clear-cut that most people likely know it to be true. "Obvious" is our answer here. "Obscured" means hidden, and "confusing" is the opposite of "obvious," so we can eliminate those choices right away. "Healthy" refers to a behavior or lifestyle that is good for your body or mind, so that choice is irrelevant here.

When someone is "oblivious," he or she is totally unaware of something. For instance, we could say, "John was totally oblivious to the fact that his mother was standing right behind him." This means that he didn't know she was there at all! While you might be tempted to think that "unintelligent" is a good synonym for this, the best option is actually "unaware"—as should be obvious, given what is the meaning of "oblivious."