问题
选择题
A good idea occurred to Mr. Baker________ to his invention recently.
A．While applying
B．While applied
C．While he was applying himself
D．While applying himself
答案
答案：C
考查主语从句。句意：最近当布克先生专心于他的发明的时候。他突然想起了一个好主意。短语：apply oneself to doing sth 专心于某事，后面是一个时间状语从句，所以选C。