until引导什么从句

Until用法详解表示“直到……为止”,两者常可换用,只是 until 比 till稍正式,所以在正式文体中,一般用 until,而在口语或非正式文体中则两者都可用.从其后所接成分来看,till多与名词或较短的从句连用,而较长较复杂的成分多用 until,位于句首时也多用 until.
两者在用法上应注意以下几点：
1.相关主句谓语必须是持续性动词,若是终止性动词,则应为否定式（因为终上性动词一旦被否定就成为状态,便可持续）.如：He waited until she was about to leave.他等着一直到她准备离开.She didn’t marry until she was over fifty.她直到50多岁才结婚.
2.引导时间状语从句时,其谓语要用现在时表示将来意义.如：I won’t leave until he comes back tomorrow.我要等他明天回来后再走.Continue in this direction until you see a sign.一直朝着这个方向走就看见指示牌了.
3.有时其后可跟副词或介词短语等.如：He has been ill until recently.他最近一直生病.Until when are you going to stay here?你在这儿要待到什么时候?We didn’t eat till past midnight.直到午夜过后我们才吃饭.She won’t go home until after the exam.她要考完试之后再回家.如果语境的需要,有时甚至可以接带有“引导词”的从句.如：Don’t leave until after I’ve spoken to you.我和你说完后再离开.
4.用于 not…until [till]…结构
(1) 若主句动词为终止性动词,其意为“直到……才……”；若主句为持续性动词,其意为“不到……就……”.比较：They didn’t find her till the next day.他们直到第二天才找到她.He didn’t wait until I returned.他没等到我回来（没等我回来他就走了）.有时 until 或 till 可以换成 before.如：Until [Before] you told me,I had no idea of it.在你告诉我之前,我对此一无所知.（即直到你告诉我,我才知道）
(2) 可用于It is (was) not until [till]…that…这样的强调句型.如：It was not until I met you that I knew real happiness.直到我遇到你以后,我才真正体会到幸福.It was not until she took off her dark glasses that I realized she was a famous film star.直到她取下墨镜,我才意识到她是一位著名影星.
(3) 若将not until [till]置于句首,其后的主句要用倒装语序.如：Not until much later did she learn who her real father was.她很久以后才知道她真正的父亲是谁.Not until he received her letter did he fully understand the depth of her feelings.他直到收到她的信之后才充分理解她的感情有多深.