Seize the chance,otherwise you will regret it.
抓住机会,要不然你会后悔的。
I was ill that day,otherwise I would have taken part in the sports meet.
那天我病了,否则我会去参加运动会的。
We didn’t know you were in trouble at that time,otherwise we would have given you a hand.
我们当时不知道你遇到了困难,要不然我们会帮助你的。