Seize the chance，otherwise you will regret it.
抓住機會，要不然你會后悔的。
I was ill that day，otherwise I would have taken part in the sports meet.
那天我病了，否則我會去參加運動會的。
We didn’t know you were in trouble at that time，otherwise we would have given you a hand.
我們當時不知道你遇到了困難，要不然我們會幫助你的。