he+didn't+go+to+bed+until+his+parents+came+back+中能把until+换成b

两者可互换使用,但含义略有不同.
一.Before表示“在… 之前”,而until表示“直到…才…”,主句肯定表示主句动作的终止时间,主句否定强调动作的起始时间.
1,主句为否定时,谓语动词为终止性动词.常见的动词有open,start,leave,go,arrive,finish,begin,stop,etc.For example:
1),The noise of the street didn’t stop before/until itwas midnight.
2),The children won’t come back until/before it isdark.
3),I didn’t leave the lonely boy before/until hismother came home.
2,主句为肯定式,谓语为延续性动词.这类动词有：stand,live,stay,talk,be,wait,etc.
For example:
1).He lived with his parents until/before he graduated from school.
2).I will wait before/until he comes to my help.
3).I shall stay here until/before you come back.
二.下列情况下宜用before不用until.
1.主句为肯定式,谓语为终止性动词时只用before.For example:
1).He fell asleep before I could take off his clothes.
2).We arrived there before it started to rain.
3).The holiday came to an end before I knew it.
4).He almost knocked me down before he saw me.