The reason he was absent was he was ill and unable to go to school.A. which; thatB. why;

问题补充：

The reason he was absent was he was ill and unable to go to school.

A. which; that

B. why; because

C. which; because

D. why; that

答案：

A. which; that

B. why; because

C. which; because

(答案→)D. why; that

解析：第一空the reason是先行词，在定语从句he was absent中作原因状语，故用why；第二空是表语从句，陈述原因的内容，而且表语从句是一个完整的句子，故用that，其不作成分，没有意思，只起连接作用。句意：他缺席的原因是他病了，不能上学了。