This is the reason he was absent.A. thatB. whichC. whyD. what

问题补充：

This is the reason he was absent.

A. that

B. which

C. why

D. what

答案：

A. that

B. which

(答案→)C. why

D. what

解析：四个引导词分别表示那个、哪一个、为什么和什么，先行词reason是原因的意思，故选C，这就是他们为什么缺席的原因。