The old professor asked us we read books in our spare time.A. whichB. thatC. whatD. if

问题补充：

The old professor asked us we read books in our spare time.

A. which

B. that

C. what

D. if

答案：

A. which

B. that

C. what

(答案→)D. if

解析：句意：那位老教授问我们在业余时间是否读书。which哪一个； that在名词性从句中没有词义； what 什么； if是否。这里是if引导的宾语从句，根据句意故选D。