Question

as is known to everybody

______is known to everybody,the Moon travels round the Earth once every month.
A:it B:as C:that D:what
A 为什么是错误的?

Answer 1

如果选择A的话,后面的句子应该是that引导的主语从句,但是题目中是用逗号隔开的单独的句子,而AS是可以直接引导这样的句子,所以选择B.
具体的可以参看AS做引导词的语法知识,没有记错的话,这属于AS引导的非限制性定语从句