The other day,my brother drover his car down the street at _____I thought was a dangerous speed.

题目

The other day,my brother drover his car down the street at _____I thought was a dangerous speed.
A.as B.which C.what D.that
如果选C的话,那请问B D为什么不能选,说明理由,要清楚哦,

答案

what I thought 是作为一个插入语,可省略,构成at a ……speed.如果用which或that,那应该改为：“……at a speed that/which I thought is dangerous.