It作形式主语 分类：句式 定义 当主语是不定式、动名词或从句时，常用it作形式主语，将真正主语后置。 结构 It + be + 形容词/名词 + (for/of sb.) + to do/that从句 例句 It is important to learn English. It is necessary that we should start early. It is kind of you to help me. It takes me an hour to get there. 相关术语 It作形式宾语 不定式 主语从句