Having checked the doors were closed andall the lights were off the boy opened the door to

问题补充：

Having checked the doors were closed,andall the lights were off,the boy opened the door to his bedroom.

A. why

B. that

C. when

D. where

答案：

A. why

(答案→)B. that

C. when

D. where

解析：that引导宾语从句,在从句中只起连接作用,不作任何成分,常被省略,但当谓语后接两个或两个以上宾语从句时,第一个that可以省略,第二个that不能省略。故选B项。why引导宾语从句意为“为什么”。when引导宾语从句，意为“当……的时候”。where引导宾语从句意为“在……地方”。