It took him four years to stage this elaborate joke simply to prove that critics do not always know what they are talkin
问题描述：
It took him four years to stage this elaborate joke simply to prove that critics do not always know what they are talking about.】
这里的IT是形式主语吗 后面的不定式才是主语 that是宾从吗 what是宾从吗
答
IT是形式主语,to stage this elaborate joke 是真正主语, that是to prove 的宾从,what是 know 的宾从