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题目
单词区别及用法
whether&if
not until&not…until

提问时间:2020-12-06

答案
whether和if的用法区别
whether与if作“是否”讲,在用法上有相同之处,也有不同之处.
一、相同之处.
1.whether和if都能引导宾语从句,常置于see,ask,learn,tell,wonder,doubt,find out等动词之后.
如:He asked me whether/is I could help him.I want to know whether/if he lives there.
2.whether和if都可用it作形式主语从句中.如:it's uncertain whether/if he'll come this evening.
3.在be uncertain/doubtful之后,常用whether引导宾语从句,有时也可以用if,如:We are uncertain whether/if Mary will come.
二、不同之处.
1.whether可置于句首引导主语从句,而if不能.如:___the 2000 Olympic Games will be in Beijing is not known yet.A.whether B.If C.Whether D.That 答案是C.
2.whether可用在介词之后,引导宾语从句,而If则不能.如:Success depends on whether we make evough effort.
3.whether可引导表语从句,if则不能.如:The puestion is whether it is not worthdoing.
4.在名词之后引导同位语从句时,用whether而不用if.如:The puestion whether the students answered correctly should be decided by the teacher.
5.whether后可接不定式,而if不能.如:Please tell us whether to go or stay here.
6.在有些动词(如discuss)之后,只能用whether,而不用if引导宾语从句.如:We discussed whether we should close the shop.
7.在引导否定概念in宾语从句时,只能用if,而不用whether.如:he asked me if I hadn't finished my work.
not until&not…until 一样啊
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