GRE Vocabulary Builder

Answer: Choice (A) is correct.

Someone who is being facetious is humorous or teasing, and someone who is earnest is serious. These are antonyms, so look for the answer pair that contains antonyms.
Choice (B) contains synonyms; supercilious means condescending and arrogant. In choice (C), urbane means suave and sophisticated - the same as debonair, so eliminate that choice. The words in choice (D) are synonyms; salubrious means healthy and wholesome. The only choice that contains antonyms is choice (A). Someone who is sanguine is confident and optimistic, not uncertain.