在介词后,一般都用whether,不用if
如:I’m thinking of whether we should go fishing.
(2)在动词 不定式前用whether,不用if
(whether to do sth.) :
例如:They asked me whether to go skating.
(3)当与or not连用,用whether,不要if
例如:I don’t know whether he’s free or not.
Mary asked whether I was doing my homework or not.
(4) 宾语从句提前时,用whether,不用if:
例如:Whether this is true or not, I can’t say.