Having checked the doors were closed,and__all the lights were off,the boy opended the door to his be

题目

Having checked the doors were closed,and__all the lights were off,the boy opended the door to his bedroom.
Awhy Bthat C when Dwhere
我的疑问是 为什么check后的that 可以省略,而and后面的that不可以省略啊?

答案