before与unless的用法区别,最好举例说明,谢谢!

我估计你要问得是before和until的区别

实际上，只要我们把握住两者使用时本身的含义及主句动词是终止性的，还是延续性的，肯定式，还是否定式两大点，就能容易地解决这类问题。现详细阐明如下：
一、在下列情况下，两者可互换用，但含义略有不同。before表示“在……之前”的意思，强 调时间先后关系；而until表示“直到……才”的意思，主句是肯定句则表示主句动作的终 止时间；主句是否定句则强调主句动作的起始时间。
1.主句为否定式终止性谓语动词。常见的动词是open,start,leave,arrive,finish,
stop等。例如：
(1)The noise of the street didn't stop until/before it was midnight.
(2)The children won't come back until/before it is dark.
(3)I didn't leave the lovely boy until/before his mother came home.
2.主句为肯定式、延续性谓语词，这类动词用stand,stay,talk,be,wait等。例如：
(1)He lived with his parents until/before he graduated from school.
(2)I will wait until/before he comes to my help.
(3)I shall stay heer until/before you come back.
二、在下列情况下，用before不用until。
1.主句这肯定式、终止性谓语动词，只用before。例：
(1)He fell asleep before I could take off his clothes.
(2)We arrived there before it atarted to rain.
(3)The holiday came to the end befor I knew i