The reason for his absence from school was he fell ill.A. becauseB. whyC. whatD. that

问题补充：

The reason for his absence from school was he fell ill.

A. because

B. why

C. what

D. that

答案：

A. because

B. why

C. what

(答案→)D. that

解析：当主语是reason时，表语从句要用that引导。