2.It+be+名词(词组)+主语从句,这类名词有:

　　a fact,a pity,a shame,an honour,a question等,如:

　　It's a pity that you missed the exciting football match.很可惜你错过了激动人心的足球比赛。

　　It remains a question whether he will come or not.他是否会来还是个问题。

　　3.It+be+过去分词+主语从句,这类过去分词有:

　　announced,believed,expected,hoped,decided,reported,said,shown等,如:

　　It is reported that 16 people were killed in the earthquake.据报道,16人在地震中丧生。

　　It is not decided who will give the operation to the patient.谁给病人做手术还不确定。

　　4.It+不及物动词+主语从句,这类不及物动词有:appear,happen,seem等,如:

　　It seemed that he didn't tell the truth.似乎他没有说实话。

　　It happened that I was out when he called.碰巧他打电话时我出去了。

　　Ⅳ.主语从句的注意事项

　　1.从句的语序用陈述语序

　　What you need is more practice.你需要的是更多的练习。

　　2.主谓一致

　　(1)从句作主语时,主句的谓语一般用单数形式,但what和who引导主语从句时,有时主句谓语的数与主句中作表语的名词的单复数保持一致。

　　What they need are books.他们需要的是书。

　　What they need is love.他们需要的是关爱。

　　(2)如果由and连接两个或两个以上的主语从句作主语时,主句的谓语动词用复数;由两个或两个以上的连接词引导一个主语从句时主句的谓语动词用单数。

　　When they will start and where they will go have not been decided yet.

　　他们将在什么时间动身以及要去哪里还没有定下来。

　　When and where the meeting will be held has not been decided.

　　会议将在什么时间以及在哪里举行还没有确定。

　　【自学效果检测】

　　找出主语从句的引导词,并分析引导词在从句中充当什么成分。

　　1.What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe.

　　2.Who will go makes no difference.

　　3.It was not immediately obvious that water was to be fundamental to the development of life.

　　4.Whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved.

　　5.Where the English evening will be held has not yet been decided.

课后提升

　　挑战一　小试牛刀

　　1.It is likely 　　　　 he is the winner of this game.很可能他是这场游戏的胜利者。

2. 　　　　 we will build a new high school hasn't been decided.