it作形式主语,which引导真正主语从句,这样的句式存不存在?
可以。比如:
It is not known which of them he will buy. 他将买其中的哪一件还不知道。
Interestingly, it is not clear which solution the prime minister favors. 耐人寻味的是,现在还不清楚首相支持哪个解决方案。