The reasonI have to go is my mother is ill in bed.A. why...whyB. why...becauseC. that...be

问题补充：

The reasonI have to go is my mother is ill in bed.

A. why...why

B. why...because

C. that...because

D. why...that

答案：

A. why...why

B. why...because

C. that...because

(答案→)D. why...that

解析：考查定语从句和表语从句：句意：我不得不走了的原因是我母亲生病在床。the reason后面跟一个定语（从句），The reason is that my mother is ill in bed. 用why引导定语从句，第二空是表语从句的连接词：原因是什么？是一个事实，这个事实用that引导，选D。