有时为了保持句子平衡，通常使用形式主语it，而将作主语的从句后置。主语从句后置且用it作形式主语的常见句型：

　　(1)It is＋名词(a fact, a pity, a shame, an honour, a/no wonder ...)＋主语从句。

　　It is a pity that we won't be able to go to the south to spend our summer vacation.

　　我们不能去南方过暑假真是太遗憾了。

　　(2)It is＋形容词(necessary, clear, strange, important, wonderful ...)＋主语从句。

　　It is important that he should know this.

　　他知道此事很重要。

　　(3)It＋不及物动词(seem, happen, appear ...)＋主语从句。

　　It seems that he has seen the film.

　　他似乎已经看过那部电影了。

　　(4)It is＋过去分词(reported, hoped, thought, said, expected, believed ...)＋主语从句。

　　It is said that he has gone to Shanghai.

　　据说他已经去上海了。

　　集中演练1

　　用适当的连接词填空

　　①What we actually need now is not a skirt but a new pair of shoes.

　　②Whether_it is true remains a question.

　　③Whoever comes will be welcome.

　　④Has it been announced when the plane are to take off?

　　⑤It is certain_that_she will do well in the exam.

语法点二 宾语从句 　　

　　1. 作动词的宾语

　　大部分宾语从句直接跟在及物动词的后面，而有些宾语从句前要有间接宾语。

　　I don't know where the post office is.

　　我不知道邮局在哪儿。

　　2. 作介词的宾语

　　(1)that引导的宾语从句仅能放在except, but等少数介词之后。

　　His account is correct except that some details are omitted.

　　除了有些细节未提到外，他的叙述是正确的。

(2)连接代词和连接副词引导的宾语从句可位于绝大多数介词之后。