高中英语重点语法:高中英语所有从句大梳理(可打印)
奇速英语2019-04-03 14:24
❷由whether,if
当由一般疑问句充当宾语从句时,用if或whether引导,意为“是否”。
如:I don't know if /whether he still lives here after so many years.我不知道这么多年后他是否还住在这儿。
但在下列情况下只能用whether,不能用if:
①在具有选择意义,又有or或or not时,尤其是直接与or not连用时,往往用whether(if…or not也可以使用)。
如:Let me know whether /if he will come or not.
(=Let me know whether or not he will come)让我知道他是否能来。
I don't know whether /if he does any washing or not.
(=I don't know whether or not he does any washing.)我不知道他洗不洗衣服。
I wonder whether we stay or whether wego.我不知道我们是去还是留。
②在介词之后用whether。
如:I'm interested in whether he likes English.我关心的是他是否喜欢英语。
We're thinking about whether we can finish the work on time.我们正在考虑是否能按时完成这项工作。
③在不定式前用whether。
如:He hasn't decided whether to visit the old man.他尚未决定是否拜访那位老人。
He hasn't decided whether to go by bus or by train.他还未决定是乘公共汽车去还是坐火车去。
④whether置于句首时,不能换用if。
如:Whether this is true or not,I can't say.这是否是真的我说不上来。
⑤引导主语从句和表语从句时宜用whether。
如:Whether she will come or not is still a question.她是否能来还是个问题。
⑥若用if会引起歧义时,则用whether。
如:Please let me know if you like the book.
可理解为:If you like the book,please let me know.你如果喜欢这本书,请告诉我。
❸只能用if不能用whether引导
(1)if引导条件状语从句,意为“如果”
The students will go on a picnic if it is sunny.
(2)if引导否定概念的宾语从句时
He asked if I didn’t come to school yesterday.
(3)引导状语从句even if(即使)和as if(好像)时
He talks as if he has known all about it.
②连接代词和连接副词引导的宾语从句
这样的宾语从句实际上是由特殊疑问句变化而来的,宾语从句要用陈述句语序。用于这种结构的动词常常是:see, say, tell, ask, answer, know, decide, show, find out, imagine, suggest, doubt, wonder, discover, understand, inform, advise等。
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