我希望在那里见到你，但如果没有，我会打电话给你。

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

记得穿旧衣服。否则，它们可能会被弄脏。

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

我们应该早点出发。否则，我们可能会错过公交车。

We should leave early. ___If ___not, we might miss the bus.