我希望在那里见到你，但如果不，我会给你打电话。

I hope to see you there but, ___if ___not, I'll call you.

记得穿旧衣服。如果不，它们可能会被弄脏。

Remember to wear old clothes. ___If ___not, they might get stained.

完成你的作业。如果不，你不能看电视。

Finish your homework. ___If ___not, you can't watch TV.