• We use whether, not if, before to-infinitives:

I don’t know whether to buy the blue one or the red one.

Not: I don’t know if to buy the blue one …

• We use whether, not if, directly before or not:

Can you tell me whether or not you’re interested in the job.

Not: Can you tell me if or not you’re interested …

• We use whether, not if, after prepositions:

[talking about a trip to Australia for a year]

We’re not interested in whether we get great jobs and that kind of thing, we just want to have a good time.

Not: We’re not interested in if we get great jobs and that kind of thing …

مطالب مرتبط:

10 اصطلاح مفید: Band 8.0+ for IELTS Speaking

صحبت از ویروس کرونا در مصاحبه آیلتس و تافل : واژه های مهم (2)