Having checked the doors were closed and all the lights were off the boy opened the do

问题补充：

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

A. why

B. that

C. when

D. ours

答案：

A. why

(答案→)B. that

C. when

D. ours

解析：that在此用于引导宾语从句，用作动词check的宾语。句中的现在分词having checked带有两个宾语从句 (that) the doors were closed和that all the lights were off，只是前面一个宾语从句省略了引导词that。