We don't know ( ) they did it.

问题描述:

We don't know ( ) they did it.
A.how B.who C.what D.which

how
这是一个考查宾语从句的题目,括号以及后面部分做know的宾语
在宾语从句中,除了that,if ,whether不做句子成分外,其他的引导词都要充当句子成分
这道题目中they did it 分别是主语,谓语和宾语,所以不用what,who,而which 做引导词通常是和后面的名词一起出现的,所以选A,我们不知道他们是怎么做的
which做引导词的给你一个例子
I do not know which book is better.