if/whether引导的从句

Question

谁能给我说一下if/whether引导的宾语从句（解释为是否）
它们的时态怎么用？我们老师说用“退步法”谁能给我详细易懂的解释一下？最好有例句。
谢谢！

Answer 1

1.当主句是一般现在时，从句可根据需要用任意时态.
The teacher wants to know if/whether the students are studying in the classroom now.

The teacher wants to know if/whether the students have finished their homework.
The teacher wants to know if/whether the students were playing football yesterday afternoon.
2·主句用过去时，从句用过去时态的一种。
He asked whether /if Tom would come to his party.
The mother wondered whether /if his son had finished his homework.
3·主句用过去时，从句是真理时，只用一般现在时
He asked whether /if the earth goes round the sun.
if,whether在宾语从句中的区别
1.介词后的宾语从句只能用whether引导,不能用if引导.
They are talking about whether they will be paid very soon.
2.whether后可以加or not,但是if不可以.
3. 在不定式前只能用whether.
He doesn't know whether to help her.

Answer 2

时态：1·主句用一般现在时，从句可用任意时。
2·主句用过去时，从句用过去某个时态。
3·主句用过去时，从句是真理时，只用一般现在时。

if,whether在宾语从句中的区别
①if和whether在作“是否”解时,引导宾语从句常放在动词know,ask,care,wonder,find out等之后,介词后一般不用if
②少数动词,如:leave,put,discuss,doubt后的宾语从句常用whether.
③whether后可以加or not,但是if不可以.
④在不定式前只能用whether.
如： I can’t decide whether to stay. 我不能决定是否留下。
⑤避免歧异时,我们常用whether而不用if.

Answer 3

有几种情况下只能用whether不能用if,
1,当句中出现or not时，用whether
2,当后面接疑问词+不定式结构时，用whether
3，在某些词后面，例如，discuss,guess,doubt,只能用whether

但是当从句出现否定式，必须用if