"Caustic" means corrosive or very critical, so "corrosive" is the correct answer. None of the other words are close in meaning to "caustic": "greedy" means excessively desirous of money; "showy" means eye-catching or gaudy; "still" means unmoving; and "unprofessional" means improper.  

"Loquacious" means talkative, so "talkative" is the correct answer. None of the other words are close in meaning to "loquacious": "blaring" means deafening; "welcoming" means hospitable; "profound" means meaningful; and "tiny" means small. 

"Fatuous" means foolish or inane, so "foolish" is the correct answer. None of the other words are close in meaning to "fatuous": "offensive" means rude; "workable" means feasible; "preventive" means preemptive; and "explanatory" means instructive.  

"Spry" means nimble, agile, or quick, so "agile" is the correct answer. None of the other answers are close in meaning to "spry": "morbid" means gruesome; "crispy" means crunchy; "fake" means not real; and "juvenile" means young.   

"Reticent" means quiet or reserved, so "quiet" is the correct answer. None of the other answers are close in meaning to "reticent": "envious" means jealous; "dangerous" means not safe; "needy" means disadvantaged or needing essentials; and "mandatory" means required.  

"Obnoxious" means extremely unpleasant, so "unpleasant" is the correct answer. "Agreeable" is an antonym of "obnoxious"; it means pleasant and easy to get along with. "Touching" means arousing strong feelings of emotion. "Prudent" means careful and cautious. "Careless" means not cautious or inattentive.

"Petulant" means bad-tempered, childish, or peevish, so "peevish," which means sullen or crabby, is the correct answer. None of the other answer choices are close in meaning to "petulant" and "peevish": "clever" means shrewd or smart; "dangerous" means potentially causing harm; "maniacal" means insane; and "challenging" means difficult.

"Peevish" means easily irritated, so "irritable," an adjective that means petulant or crabby, is the correct answer. None of the other answer choices are close in meaning to "peevish" and "irritable": "visible" means able to be seen; "amiable" means friendly or easy to talk to or get along with;"apathetic" means unconcerned or indifferent; and "orderly" means arranged in a neat and tidy manner.

"Affable" means easy to get along with or friendly. "Odorous" means having a bad smell. "Vulnerable" means weak or helpless. "Dull" means boring or not interesting. "Canine" refers to dogs and their characteristics.

"Humane" means showing compassion or emotion. "Foolish" means stupid or silly. "Pacific" means calm and peaceful. "Hydrous" means having water or referring to water. "Barren" means lifeless or incapable to growing crops.