5.关于形式主语it

据上所述，主语从句可以置于主语的位置，也可以用形式主语it先行，把真正的主语从句后置。但是在下面的情况下，只能采用it先行。

提示：

除了that引导的主语从句外，其他连接词引导的主语从句也可以被it代替。

(1)在“It+be+过去分词(said，reported，thought，expected，believed，decided，known，announced，arranged，suggested，ordered，etc．)+that或其他连词”引导的从句中。

It is not yet known how these were conveyed over a distance of 380 kilometres．(人教大纲版高二下第76页)

至今还不知道这些石头是如何从380公里以外的地方运过来的。

It is sometimes said that a society can be judged by the way it cares for its weakest members．(人教大纲版高三第75页)

有时候人们说，一个社会的好坏可以从它对弱势群体的照顾来判断。

It was thought that the trip could take up to 13 days to complete．(人教大纲版高三第53页)

当时认为这个行程可能要花13天才能走完。

It has been proved that the copper knives came fromplaces as distant as Spain and western France．(人教大纲版高二下第76页)

事实已经证明，铜刀是来自像西班牙或法国西部那样遥远的地方。

It is suggested that the meeting(should)be put off．

建议把会议推迟。

(2)主句是疑问句或感叹句时。

But is it really true that we are living in the“Information Age”?(人教大纲版高二下第62页)

但是我们是不是的的确确生活在“信息时代”中了呢?

How wonderful it is that we'll visit the Great Wall tomorrow!

我们明天去参观长城，真是太好了!

Does it matter much that they will not come tomorrow?

他们明天不来很要紧吗?

How strange it is that the children are so quiet!

孩子们这么安静真奇怪!

(3)主句谓语动词是appear，seem，turn out，happen，occur，strike，follow，matter等时。

It(so)happened that she had a cold and didn't go with us that day．

那天碰巧她感冒了，所以没有跟我们一起去。

It turned out that I was wrong．

结果证明我错了。

It seems that this test is reliable．

看来他的检测是可信的。

(4)在“It+be+形容词(obvious，necessary，important，astonishing，unbelievable，true，natural，surprising，good，wonderful，funny，possible，unlikely，likely，possible，impossible，certain，probable，etc．)+that或其他连词”引导的从句中。

It is certain that she will do well in her exam．

毫无疑问她考试的成绩会很好。

It is probable that he told her everything．

很可能他把一切都告诉她了。

It is astonishing how widely English is used．

英语使用的程度之广泛是惊人的。

It is necessary that he should do so．

他必须这样做。

It was unbelievable how much water came down on the ship．(人教大纲版高二上第76页)

大量的海水砸向轮船，真是太难以置信了。

It is important that we(should)learn English well．

学好英语对于我们来说是很重要的。

(5)在“It+be+名词词组(no wonder，an honor，a good thing，a pity，no surprise，a wonder，etc．)+that等连词”引导的从句中。

It is also a mystery how early man was able to construct Stonehenge without the use of modern construction machines and lorries．(人教大纲版高二下第76页)

早期的人是如何在不用现代化建筑机械和货车的情况下来建造这个巨石阵的，这仍然还是一个谜。

It's a pity that we can't go．

很遗憾我们不能去。

It's no surprise that our team should not have won the game．

我们没赢这场比赛真意外。

It is small wonder that their team has won．

他们队赢了不足为怪。

(6)在“It+doesn't matter(makes no difference，etc．)+连接代词或连接副词”引起的主语从句中。

It doesn't matter if your guesses are wrong．(人教大纲版高三第206页)

即使你猜错了也没有关系。

It doesn't matter whether she will come or not．

她是否来无关紧要。

It makes no difference where we shall have the meeting．

我们在哪里开会都是一回事。