a. It + be +形容词+ that-从句

It is necessary that…　　　 有必要……

It is important that…　　　 重要的是……

It is obvious that…　　　　 很明显……

b. It + be + -ed 分词+ that-从句

It is believed that…　　　　　人们相信……

It is known to all that…　　　 从所周知……

It has been decided that…　　 已决定……

c. It + be +名词+ that-从句

It is common knowledge that…　 ……是常识

It is a surprise that…　　 令人惊奇的是……

It is a fact that…　　　　 事实是……

d. It +不及物动词+ that-分句

It appears that…　　　　　　似乎……

It happens that…　　　　　　碰巧……

It occurred to me that…　　 我突然想起……

17.3 名词性wh-从句

1)由wh-词引导的名词从句叫做名词性wh-从句。Wh-词包括who, whom,. whose, whoever, what, whatever, which, whichever等连接代词和where, when, how, why等连接副词。Wh-从句的语法功能除了和that-从句一样外，还可充当介词宾语、宾语补语和间接宾语等。例如：

主语： How the book will sell depends on its author.　书销售如何取决于作者本人。

直接宾语：In one's own home one can do what one likes.　在自己家里可以随心所欲。

间接宾语：The club will give whoever wins a prize.　获胜者俱乐部将颁奖。

表语： My question is who will take over president of the Foundation.　我的问题是谁将接任该基金会主席职位。

宾语补足语：She will name him whatever she wants to. 她高兴给他起什么名字就取什么名字。

同位语：　　I have no idea when he will return.　 我不知道他什么时候回来。

形容词宾语：I'm not sure why she refused their invitation.　 我尚不能肯定她为什么拒绝他们的邀请。

介词宾语：　That depends on where we shall go. 那取决于我们去哪儿。

2)Wh-从句作主语也常用先行词it做形式主语，而将wh-从句置于句末。例如：

It is not yet decided who will do that job.　 还没决定谁做这项工作。

It remains unknown when they are going to get married.　 他们何时结婚依然不明。

17.4 if, whether引导的名词从句

1)yes-no型疑问从句

从属连词if, whether引导的名词从句是由一般疑问句或选择疑问转化而来的，因此也分别被称为yes-no型疑问句从句和选择型疑问从句，其功能和wh-从句的功能相同。例如：

主语：Whether the plan is feasible remains to be proved. 这一计划是否可行还有等证实。

宾语：Let us know whether / if you can finish the article before Friday. 请让我们知道你是否能在星期五以前把文章写完。

表语：The point is whether we should lend him the money. 问题在于我们是否应该借钱给他。

同位语：They are investigating the question whether the man is trustworthy.　他们调查他是否值得信赖。

形容词宾语： She's doubtful whether we shall be able to come. 她怀疑我们是否能够前来。

介词宾语： I worry about whether he can pass through the crisis of his illness. 我担心他是否能度过疾病的危险期。

2)选择性疑问从句

选择性疑问从句由关联词if/whether…or或whethe…or not构成。例如：

Please tell me whether / if they are Swedish or Danish. 请告诉我他们是瑞典人还是丹麦人。

I don't care whether you like the plan or not. 我不在乎你是否喜欢该计划。

17.5 否定转移

1)将think, believe, suppose, expect, fancy, imagine等动词后面宾语从句的否定词转移到主句中，即主句的谓语动词用否定式，而从句的谓语动词用肯定式。例如：

I don't think I know you.　我想我并不认识你。

I don' t believe he will come.　我相信他不回来。

注意：若谓语动词为hope,宾语从句中的否定词不能转移。例如：

I hope you weren't ill. 我想你没有生病吧。

2)将seem, appear 等后的从句的否定转移到前面。例如：

It doesn't seem that they know where to go. 看来他们不知道往哪去。

It doesn't appear that we'll have a sunny day tomorrow. 看来我们明天不会碰上好天气。

3)有时将动名词，介词短语或整个从句的否定转变为对谓语动词的否定。例如：

I don't remember having ever seen such a man.　我记得从未见过这样一个人。(not否定动名词短语 having…)

It's not a place where anyone would expect to see strange characters on the street.

在这里，人们不会想到在街上会碰上陌生的人。(anyone 作主语，从句中的谓语动词不能用否定形式。)

4)有时状语或状语从句中否定可以转移到谓语动词前。例如：

The ant is not gathering this for itself alone.　(否定状语)　蚂蚁不只是为自己采食。

He was not ready to believe something just because Aristotle said so. (否定because状语)

他并不因亚里斯多德说过如何如何，就轻信此事。

She had not been married many weeks when that man's younger brother saw her and was struckby her beauty.(否定状语many weeks)　她结婚还不到几个月，这个人的弟弟就看见她了，并对她的美

貌着了迷。