"Inexorable" is an adjective that means "impossible to stop or prevent," or when describing a person, "impossible to persuade by request or entreaty." So, neither "preventable" nor "persuadable" can be the correct answer because each of those words is an antonym of "inexorable," not a synonym. The correct answer is "unstoppable," an adjective that like "inexorable" means "impossible to stop or prevent."

Both "miniscule" and "modicum" mean a small amount so they are not correct. "Lucid" means clear, and a "hedonist" is someone who lives for pleasure. "Gargantuan" is a synonym for huge.

The word “economical” is not the same as “economic,” which can mean “pertaining to finances or wealth.” Instead, it can mean “someone who is thrifty or careful with money” as well as “something that is inexpensive but useful” such as “an economical house.”

The word “sheer” is not the same as “shear.” The latter means “to cut” or “to shave,” often speaking of the cutting of wool from sheep. The word “sheer” means instead “complete” or “sudden.” The latter would be used to describe something like a cliff that is completely vertical—“a sheer drop.” Likewise, it can mean “complete,” “utter,” “or “absolutely” when used in an expression like, “The plan was not merely questionable; it was sheer madness to do something so insane.”

“Affluent” means very wealthy. It is the opposite of “impoverished,” which means very poor. “Despicable” means evil and wicked; “comely” means very cute and beautiful; and “winsome” means charming and appealing.

“Colloquial” means informal or conversational and refers to language or writing, so "conversational" is the best answer choice. As for the other answer choices, “irredeemable” means unable to be redeemed or so bad that it cannot be forgiven; “plausible” means believable as being potentially true or succeeding; “irrational” means not rational, not logical, and thinking with emotions; and “illicit” means against the rules or illegal.

"Caustic" means corrosive when describing substances or scathing when describing communication and speech. So, "derisive," which means disdainful and scathing, is the correct answer. “Plump” means fat, chubby, and round; “euphoric” means in a state of intense happiness; “obscure” means esoteric or unclear; and “obligatory” means mandatory.

“Authoritarian” describes governments and means autocratic, repressive, or “tyrannical.” As for the other answer choices, “democratic” means relating to democracy and its form of representative government; “liberated” means set free; “enslaved” means made a slave; and “royal” means a king, a queen or related to a king or queen.

You might be tempted to see the word “arbiter” in “arbitrary.” They are not unrelated, for both pertain to a judgment being made. However, when something is "arbitrary," it is done at the whim of the one judging. It has no real reason other than that person’s desires or passions. Therefore, an “arbitrary” decision could be called “whimsical.” All of the other answers (except “flimsy”) are meant to trick you.

The word "affluent" does have roots that mean to flow. While this meaning was once upon a time reflected in the word, it no longer is used in this manner. Instead, the word means wealthy—as though someone is "flowing" with money. Thus, the only option that is appropriate is "prosperous."  (Note that "mobile" is not the same as flowing. A walking person is mobile—yet is not flowing, strictly speaking.)