You must study hard while (you are) young, or you will regret when (you are) old. 趁年轻时要努力学习,不然到老了你会后悔的。
I won't go unless (I am) invited. 我不会去, 除非请我。
Look out for cars when (you are) crossing the streets. 过马路时要注意汽车。
While (I was) waiting I was reading some old magazines. 等的时候我在看一些旧杂志。
He worked very hard though (he was) still rather poor in health. 尽管身体还不好,但他仍努力工作。
He will work hard wherever (he is) sent by the Party. 无论党把他派往哪里,他都会努力工作。