Which figure of speech is used in the idiom as dead as a doornai

Which figure of speech is used in the idiom as dead as a doornail?（ ）
A、Personification.
B、Metaphor.
C、Simile.
D、Synecdoche.
【正确答案】：C
【题目解析】：本题考查习语使用的修辞手法。personification：拟人；metaphor：暗喻；simile：明喻；synecdoche：借代。as dead as a doornail字面意思是“死得像门钉一样了”，指的是被彻底遗忘或废弃的，此处使用了明喻的修辞手法。故C选项符合题意。