Think that you know---in fact you don’t is not a good idea.如

Think that you know___in fact you don't is not a good idea.如题
A.what B.that C.when D.which

Think you know (what) in fact you don't is not a good idea. 认为你知道你并不知道的事实,可不是个好事哦. you know后面加句子,这是没有错的.可是这里的意思事要表达你知道你并不知道的,所以它需要加上宾语.这个句子可拆成： Think you know it. 和 in fact, you don't know it.可以知道这个句子就是缺少了宾语,而选项中只有what能够做宾语.
麻烦采纳,谢谢!