When he was awake,he found that he was standing on ____ seemed to be a piece of stone.

问题描述:

When he was awake,he found that he was standing on ____ seemed to be a piece of stone.
A.that B.what C.which D.it

B what
what在这既做前句he was standing on 的宾语也引导后面从句,相当于something that.只有what能同时在两个从句中做成分