In this multiple choice question, the options are:
A) proclivity
B) petrous
C) taciturn
D) trenchant
In order to answer that question, you just need to know the definitions of these words. Proclivity means tendency, predisposition; petrous means like a stone; taciturn is calm and trenchant is energetic. Trenchant is the correct answer. In a broader explanation, if you're trenchant, it means you think smart and say smart words, that goes right into the heart of the matter.