名词性从句包括:主语从句、表语从句、宾语从句、同位语从句。
(一)主语从句知识要点
1.从句作主语时,谓语动词用单数。
Who will be sent there has not been decided yet.
Whether Mr GREen has got the letter or not is not known.
但下列两种情形应视具体情况而定:
①what引导的主语从句应视what所指的意义来确定。what指的是单数时,谓语动词用单数;what指的是复数时,谓语动词用复数。试比较:
What they need is more money/help/advice/information.
What they need are more men/mobile phones/TV sets/computers.
②两个或两个以上的从句并列作主语时,应视其意义而确定谓语动词的单、复数形式。其作为一个整体指代同一内容时为单数;其作为两个以上不同内容时为复数。例如:
Whether we'll go and help them and how we can help are not the same.They are quite different.
Where they are going to build the dam and how is the biggest problem to be discussed at the meeting.
2.主语从句通常情况下可使用it做形式主语,而将从句置于句末。例如:
It is being looked into who broke the window.
It is not clear whether he will leave for London or not.
It is necessary that we should send more food to the flooded area.
It is not known yet when the plane will take off.
但what及带-ever类疑问词引导的主语从句不能用it 代替其作形式主语。例如:
[误] It is not right what he said.
[正] What he said is not right.
[误] It is becoming popular among the young students whatever he wrote.
[正] Whichever book he wrote is becoming popular among the young students.
当带主语从句的句子是疑问式,则凡能使用it作形式主语的都必须使用这一结构。例如:
Has it been announced when the plane is to take off?
Is it made clear that everyone must be cautious about SARS?
对于上述那些不能用it代替其作形式主语的,则无须如此。例如:
Is what he said true?
3.who和whoever均可引导主语从句,但两者引导的主语从句有以下两点区别:
①Who引导的主语从句是整个句子作主语,指的是某一件事情或情况;而whoever引导的主语从句是人作整个句子的主语,而不是整个句子。试比较:
Who has broken the window is not found out yet.(是“谁打碎玻璃”这件事情尚未查清)
Whoever has broken the window must pay for it.(是打碎玻璃的人必须赔偿,该句相当于Anyone/The person who has broken the window must pay for it.)
②Who引导的主语从句可以用it作形式主语,而whoever引导的主语从句则不能。试比较:
Who will be sent to study abroad is not decided yet.=It is not decided who will be sent to study abroad.
Whoever will be sent to study abroad should hand in two photos before Friday.(该句不可改写为:It should hand in two photos before Friday whoever will be sent to study abroad.)
4.引导主语从句只能使用whether,不能使用if。例如:
Whether the mid-term exam will be put off is not decided yet.
[误] It is not clear yet if the Chinese football team can win the game.
5.在it is a pity (shame),it is strange,it is no wonder等结构后的主语从句中应使用虚拟语气。例如:
It is a GREat pity that he should be so careless.
It is strange that they should have lost the match.
