“Frivolous” means purposeless and foolish, often specifically when serious purpose was expected. Thus, the correct answer is "inane," which means goofy and idiotic. As for the other answer choices, "listless" means languid or lethargic; "dour" means dreary and stern; "aristocratic" means having to do with historical high classes; and "pliable" means able to be bent.

The “margins” of a piece of paper are the edges on which nothing is normally written. When someone takes “marginal notes,” he or she writes in this space—as when someone writes in the margins of a book to keep notes on the text being read. To say that something is “marginal” is to imply that it does not sit “in the midst of the important things” but is merely “on the edges.” For this reason, the word is often used to describe something that is believed to be unimportant. For example, someone might say, “His remarks were really of marginal significance for the decision, for he did not know much about the topic.”

"Monumental" means very large or very important, so "significant" is the answer choice closest in meaning to "monumental." As for the other answer choices, "atrocious" means terrible and evil, "petrified" means turned to stone or so afraid that one cannot move, "statuesque" means stately and beautiful, and "fervent" means zealous.

"Negligible" means insignificant or unimportant. "Thrifty" means economical or frugal. "Canceled" means called off or erased. "Viable" means reasonable or practical. "Sarcastic" means nasty or mocking in speech. 

"Expendable" means superfluous or unnecessary. "Erudite" means well-educated and cultured. "Dogmatic" means dictatorial or opinionated. "Pedantic" means bookish or overly precise. "Extravagant" means lavish, indulgent, or wasteful. 

"Superficial" and "perfunctory" both mean shallow or trivial. "Analytical" means systematic or examining. "Genuine" means authentic or real. "Profuse" means abundant or excessive. "Somber" means sad or depressing. 

"Elaborate" and "intricate" both mean detailed or complicated. "Facile" means easy or effortless. "Inveterate" means long-standing or established. "Concise" means short and to the point. "Morose" means depressed or pessimistic. 

The word “negligible” is related to “neglect,” though it does not directly mean that. When something is “negligible,” there is so little of it that it is not even worth being thought about. That is, one can neglect thinking about it. It would be used in a sentence like, “The health benefits of running an extra three miles on top of his regular five were so negligible that he decided to forego the extra exercise.” The sense is that they are “insignificant.”

"Ancillary," when used as an adjective, means "providing necessary support to the primary activities or operation of an organization, institution, industry, or system," or "additional; subsidiary." So, "necessary" cannot be the correct answer because it is an antonym of "ancillary." "Supplemental," an adjective that means "something that completes or enhances something else when added to it," is the answer choice closest in meaning to "ancillary," so it is the correct answer.

“Superfluous” means extraneous and unnecessary, so "unnecessary" is the correct answer. As for the other answer choices, “poignant” means touching or moving, making one feel that something is sad and meaningful; “pompous” means arrogant and self-obsessed; “garrulous” means talkative; and "cordial” means polite.