I'll back you up if they don't believe you.

如果他们不相信你，我会为你作证。

《牛津词典》

What's our fallback if they don't come up with the money?

要是他们拿不出钱，我们如何应变？

《牛津词典》

People who message a lot feel unpopular if they don't get many back.

如果发送许多短信的人并未得到很多回复，他们会觉得自己不受欢迎。

《柯林斯英汉双解大词典》

"If they don't get injections or oxygen from the Ministry of Finance, then this patient would die."

VOA: standard.2010.04.23

But, you know, any professor who stands before you should say the same thing about his or her subject. If they don't believe that, they shouldn't be teaching.

但是，你知道，所有站在你们面前的老师,可能都会这样介绍他的课程,如果他们不那样相信着，那他们就不应该教那门课了。

麻省理工公开课 - 固态化学导论课程节选

And secondly, I think that, even if they don't know how to do a problem,

二是，我觉得，即使他们不知道怎么做一道题，

体罚是不可取的 - SpeakingMax英语口语达人

If they don't get as much as Gerald Corbett, how much should they get?

BBC: George Muir and Stuart Francis

Some explained, even if they don't personally believe in the practice, their relatives take it seriously.

CNN: Witchcraft in Tanzania: the good, bad and the persecution

If they don't learn these things, their food will just end up on the floor.

BBC: NEWS | UK | Education | 'Good' food provided in childcare