having checked the doors were closed,and __ all the light were off ,the boy opened the door to his bedroom 。为什么and 前要打逗号,如果不打就是两个并列结构,填that就可以,但是打了不是说明两个句子?!
第1个回答 2013-04-06
逗号打不打不影响这个句子的结构，and连接的是两个that引导的宾语从句做having checked的宾语，第一个that可以省略，后面的不能省略。主干结构是the boy opened the door to his bedroom 。
