爱华网第一部分
常规主语从句，即句子在复合句中充当一个主语
主语从句的时态不受主句时态的影响和限制
(1)That he finished writing the composition in such a short time surprised us all.
(2)Whether we will go for an outing tomorrow remains unknown.
(3)Who will be our monitor hasn't been decided yet.
(4)Whom we must study for is a question of great importance.
(5)What caused the accident remains unknown.
(6)Whatever you did is right.
(7)Whom the watch belongs to is unknown.
(8)What we need is time.
(9)What we need are good doctors.
名词性从句的时态规则：
1)、主句谓语动词是现在或将来时，从句谓语动词可以用任何需要的时态。
I wonder what he is doing now.
Do you know when and where he was born?
I'll write to tell him where I 'll meet him.
2)、主句谓语动词是过去时，从句谓语动词一般需用过去时。
(1)从句与主句的谓语动作同时发生，从句用一般过去时或过去进行时。
I thought that he studied hard.
He told me his son was watching TV.
(2)从句谓语动作在主句谓语动作之后，从句用过去将来时。
He said he would spend his holidays in Qingdao.
(3)从句谓语动作在主句谓语动作之前，从句用过去完成时。
They told me they had waited for me half an hour.
(4)从句如果有表示过去某一具体时间的状语，仍用过去时。
She told me her brother died in 1945.
3)客观的条件，从句时态不受丝毫影响。
(1)从句说明的是不受时间限制的事实或真理(客观真理)。
The teacher told us that the earth turns from west to east.
He said Asia is the largest continent.
It was true that water freezes at thirty-two degrees Fahrenheit.
(2)当从句表示的是反复出现的时态不变。
She told me that she gets up at six o'clock every morning.
He asked me when the train usually starts.
(3)当从句是用来表达解释科技内容时时态不变。
(4)当从句的谓语动作仍在继续时，或者表示现在仍在的状态时，时态不变。
He said that the workers in that factory are trying to fulfill the task in time.
She told me the other day that she is only 10.
(5)当从句的动作状态还未发生，要用一般式表示。强调与现在的联系。
He said he will wait for me this evening.
小结:
(1)引导主语从句连词有that,whether,who,what,whatever等
(2)连词位于句首不能省略
(3)主语从句大多数情况下视为第三人称单数，但也有例外，如例(9)
注意：当what引导的名词性分句作主语时，主谓一致问题极为复杂。著名学者周海中教授在论文《关于what-分句作主语的主谓一致问题》中就这一问题做了深入研究，并给出了10种的主谓一致关系。这些一致关系值得英语学习者和使用者特别注意。
第二部分
为了防止句子头重脚轻，通常把形式主语it放在句首位置，真正主语搁置于句末
(1)It is certain that he will win the match.
(2)It is true that he has made a very important discovery in chemistry.
(3)It is very likely that they will hold a meeting.
(4)It is strange that he should do that.
(5)It is important that we all should attend the meeting.
(6)It is strange that the man should have stuck to his silly ideas.
(7)It is a pity that we won't be able to go to the south to spend our summer vacation.
(8)It is still a mystery what caused the accident.
(9)It is said that he has gone to shanghai.(=He is said to have gone to shanghai)
(10)It is known to all that the gun powder was first invented by the Chinese.
(11)It is suggested that the work should be done with great care.
(12)It happened that the two cheats were there. (=The two cheats happened to be there)
小结:
(1)为避免头重脚轻，常以形式主语it引导从句。 It+形式主语谓语+从句。
(2)由于主语从句一般被认为是单数形式，形式主语的谓语动词、be动词+表语 均为单数第三人称形式或过去式.
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