1．名词性从句必须是陈述句语序。例如: I don’t know which book I should borrow from the library．我不知道从图书馆借哪本书。That is why he came here．这就是他来这儿的原因。2．主语从句、宾语从句如果太长,要把它们放在句子后面,前面用it作形式主语或宾语,这样使句子保持平衡。例如: 1. Noun clauses must be declarative sentences. For example: I don’t know which book I should borrow from the library. I don’t know which book to borrow from the library. That is why he came here. This is why he came here. 2. If the subject clause or the object clause is too long, they should be placed behind the sentence. In front of it, use it as a form subject or object, so that the sentence is balanced. E.g: