注意点: it 构成的主语从句 （1）由连词 that 引导的主语从句，在大多数情况下会放到句子的后面，而用代词 it 作形式主语。 例如：That light travels in straight lines is known to all. =It is known to all that light travels in straight lines.
When the plane is to take off has not been announced . = It has not been announced when the plane is to take off. (但当 what 引导的主语从句表示“?的东西”时，一般不用 it 作形式主语。) 错:It is a book what he wants. 对:What he wants is a book. 另外，需要注意的是，it 作形式主语代替主语从句时，要注意和 as 引导的定语从句的区别。试比较： It was reported that the US was under the terrorist attack. As was reported, the US was under the terrorist attack. （2）常见用 it 作形式主语的复合句结构 <a> It is +名词+从句 It is a fact that? 事实是?? It is good news that ? ??是好消息 It is a question that ? ??是个问题 It is common knowledge that ? ??是常识 类似的名词还有：a pity；a wonder；a good thing； no wonder； surprise 等。 例如：It is a mystery to me how it all happened. It is common knowledge that the whale is not a fish. It is no surprise that Bob should have won the game. It’s a pity that you missed the film. <b> It is +形容词+从句 It is necessary that ? 有必要?? It is clear that ? 很清楚?? It is likely that ? 很可能?? It is important that ? 重要的是?? 类似的形容词还有：strange; natural; obvious; true; good; wonderful; possible; unlikely; quite; unusual; certain; evident; worth-while; surprising; interesting; astonishing, etc. 例如：It is doubtful whether she will be able to come. It was really astonishing that he refused to talk to you. It is essential that he should be here by the weekend. It seems obvious that we can not go on like this. It is necessary that you （should）master the computer. It is important that a student learn English well. It’s clear that they badly need help. It is likely that a hurricane will arrive soon. 需要注意的是，这类主语从句中，谓语动词很多为“ （should）＋动词原形” ，即要用虚拟语气。 <c> It is +过去分词+从句 It is said that ? 据说?? It is reported that ? 据报道??
It has been proved that ? 已证明?? It must be proved that? 必须指出?? 类似的过去分词还有：known; estimated; expected; believed; thought; hoped; noted; discussed; required; decided; suggested; demanded; made clear; found out,etc. 例如：It is thought that he is the best player. It is estimated that the vase is 2000 years old. It is used to be thought that a new star must be due to a collision between two stars. It has not been made clear when the new road is to be opened to traffic. It is said that he was killed in the earthquake. <d> It seems （happened / appears / doesn’t matter / makes no difference / occurred ?）that ? 如： It seems that they will win the game. It makes no difference whether he will attend the meeting or not. It does not matter if I missed my train. It happened that I saw him yesterday. 一．找出下列句子中的主语从句及其引导词，并且指出引导词是否充当成分，充当什么成分。 1. That we shall be late is certain. 2. That the driver could not control his car was obvious. 3. It is certain that we shall be late. 4. It was obvious that the driver could not control his car. 5. Is it possible that they will come tomorrow？ 6. It is clear that he was telling the truth. 7. It’s probable that we’ll be a little late. 8. What caused the accident is a complete mystery. 9. It worried her a bit that her hair was turning grey. 10. It shocked me that Peter didn’t tell anybody where he was. 11. Who was responsible for the accident is not yet clear. 12. It’s a pity that you can’t go with us. 13. What he did is not yet known. 14. It is said that he has been there many times. 15. It is not yet clear who was responsible for the accident. 三．用适当的引导词填空。 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. ______ she bought so many dictionaries is not clear. = It is not clear _____ she bought so many dictionaries. 不清楚她为什么买这么多字典。
3. ________ he was admitted into Beijing University made his teachers and parents happy. 他考上了北大，这让他的老师和父母很高兴。 4. It’s a pity________ you can’t attend my birthday party. 很可惜你不能参加我的生日聚会。 5. _________ we will build a new high school hasn’t been decided. 我们是否要建新高中还没决定呢。 6. __________ breaks the law should be punished. 不管谁违法都应该受到惩罚。 三．选择题。 1. _____ as much as one-fifth of all timber harvested is not used. A. The estimate 估计 B. The estimated C. They are estimated D. It is estimated that 2. _____ some mammals came to live in the sea is not known. A. Which B. Since C. Although D. How 3. _____ we have achieved is attributed to the guidance of our parents. A. Whoever B. Whatever C. However D. That 4. _____ wealthy does not necessarily mean that a man is greedy. A. For the reason that he is B. Just because he is C. The reason of being D. That he is 5. Although ___ happened in this developed country sounds like science fiction,
it could occur
elsewhere in the world. A. which B. what C. how D. it 6. _____ she had forgotten to take her notebook. A. That occurred to her B. She occurred that C. To her that occurred D. It occurred to her that 7. I am sure that _____ she said is wrong. A. which B. all C. this D. what 8. We lost our way in the forest, and ____ made matters worse was that it was getting dark. A. that B. which C. it D. what 9. _____ or not is still uncertain. A. He’s coming B. If he is coming C. That coming D. Whether he’s coming 10. It’s _____ he’ll be able to come. A. doubt whether B. doubtful C. doubt it D. doubtful whether 11. ______ he is at work in the heart of the big city or at home in the quiet ick’s life is tied to machines. A. Whether B. Till C. If D. Unless 12. _____ he saw both surprised and frightened him. A. That B. When C. What D. Which 13. _____ is warm sunshine. A. What do we all need. B. What all we need C. What we need D. What we all need
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