1、call a taix,and you'll catch the train.
Call a taxi, or you'll miss the train.
2、she can't finish the hard work on time without your help .
She can't finish the land hard work on time if you don't help.
3、work hard,and you will pass this exam .
Unless you work hard,you won't be able to pass this exam.
4、hurry up, or you'll be late.
If you hurry up,you won't be late.
If you don't hurry up,you will be late