It seemed that he was very happy.这句子的成份该如何分板,it是什么成份?主谓宾都分别是什么?

这个句子原本是这样的：It(形式主语） seemed （系动词）to be true （表语）that he was very happy（主语从句）可后来,随着语言的演变,就成了现在这样子了It （主语, 无意义）seemed（系动词） that he was very h...