1． It作先行主语和先行宾语的一些句型
    
    She had said what it was necessary to say.
    
    2． 强调句型
    
    It is not who rules us that is important, but how he rules us.
    
    3． "All+抽象名词"或"抽象名词+itself"（very+形容词）
    
    He was all gentleness to her.