The doctor ______his temperature before he_____to his chest.

题目

The doctor ______his temperature before he_____to his chest.
a.has taken;listened b.had taken;listened c.took;had listened d.took;listened
是哪个?为什么呢?

答案

b,had发生于vt-ed之前.过去完成时发生于一般过去式之前