句法结构句子成分She smiled.Seeing is believing.I am reading books.To study hard is important.主语（subject)主语是句子所要描述或者表达的主体，是动作的发出者，一般是一个名词或者名词性成分。I will watch the movie.He borrowed my keys.Time flies.He can play basketball.I am reading books.She is beautifu...