I. Choose one correct answer for the following questions 【單選題】每題 1 分，共計 60 分，答錯 1 題倒扣 0.25 分，倒扣至本大題零分為止，未作答，不給分亦不扣分。 1. What is the carbon nucleophile which attacks molecular bromine in the acid-catalyzed α-bromination of a ketone? (A) an enol (B) a Grignard reagent (C) an acetylide (D) a carbocation (E) an enolate