题目内容：

We all know__is the to__ A.work hard;success B.work hard;succeed C.to work hard;success D.
We all know__is the to__
A.work hard;success B.work hard;succeed C.to work hard;success D.to work hard;succeed

优质解答

C
We all know_to work hard (从句中做主语）_is the (key) to_success(to 的宾语,用名词）_
我们都知道,勤奋是成功的关键