一、that,whether / if的选择
1. that 用于表示肯定含义的从句中,whether / if 表示疑问, 用于表示疑问的从句中。
例1: It worried her a lot ____ her hair was turning grey.
A. while B. if
C. that D. for
[析]:既然令她如此担心,应是肯定的事实,故答案选C。
例2: ____ we’ll go camping tomorrow depends on the weather.
A. If B. Whether
C. That D. Where
[析]:既然看天气而定,答案应为B。If引导名词从句作主语时不能置于句首。
2. 若doubt 一词作“怀疑”解,接宾语从句时,主句为肯定形式时用whether或if,主句为否定或疑问形式时用that。
例1: I doubt whether he will come soon.
例2: I don’t doubt that he will come soon.
例3: Do you doubt that he will come soon?
注意:当doubt 做“认为……未必可能”时,只能用that。
例4: I doubt that he will come.
二、that的省略与否
1. that连接主语从句,置于句首时不能省略。
例: ____ he has gained admission to Beijing Normal University has spread all over his village.
A. / B. Whether
C. That D. When
[析]:主语从句表示的是一个事实,应选that, 而that 不能省略,故选C。
2. that连接宾语从句可以省略,但若有两个that从句,则第二个从句中的that不可省略,如下面例1;另外作为介词后引导宾语从句的连词that也不能省略,如例2。
例1: I don’t believe (that) he has ever read any of Shakespeare’s works or that he has ever heard of him.
例2: His composition is very good, except that there are some spelling mistakes.
3.如that连接的宾语从句中紧接着有一其他连词连接的状语从句,that不能省略。
例: He said that, if I did not have time, I might choose not to go.
4.引导同位语从句的连词that不省略。
例: The news that our team has won the match is true.
5.引导表语从句的连词that不可省略。
What he suggested is that you (should) study harder than ever before.
三、 连词whether和if的选择
1.连词whether和if均可使用的情况:
(1) 引导宾语从句。例如:
I wonder if / whether the news is true.
(2) 在“be adj.”之后。例如:
He was not sure whether / if it is right.
2.只能用whether,不能用if的情况:
(1) 在表语从句和同位语从句中。
例1: The question is whether the film is worth seeing.
例2: The news whether our team has won the match is unknown.
(2) 在主语从句中,如果用it作形式主语,whether和if都能引导主语从句,否则,只能用whether。
例1: It hasn’t been decided whether / if we shall attend the meeting.
例2: Whether we shall attend the meeting hasn’t been decided yet.(不可用if)
(3) 在介词之后(介词往往可以省略)。
例:It all depends (on) whether they will support us.
(4) 后面直接跟动词不定式时。
例: He doesn’t know whether to stay or not.
(5) 后面紧跟or not 时。
例:We didn’t know whether or not she was ready.
(6) 正式文体中,句中有or not 时,只能用whether。
(7) 用if会引起歧义时。
例: Please let me know if you like it.
[析]:该句有两个意思:“请告诉我你是否喜欢。” 或“如果你喜欢,请告诉我。” 用了whether 就可以避免歧义。
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