19.9 比較until和till
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　　此兩個連詞意義相同?？隙ㄐ问奖硎镜囊馑际?做某事直至某時"，動詞必須是延續(xù)性的。否定形式表達的意思是"直至某時才做某事"。動詞為延續(xù)性或非延續(xù)性都可　以。 正確使用這兩個連詞的關(guān)鍵之一就在于判斷句中的動詞該用肯定式還是否定式。
　
　 肯定句：
　 I slept until midnight. 我一直睡到半夜時醒了。
　 Wait till I call you.　 等著我叫你。
　 （在肯定句中可用before代替 Let's get in the wheat before the sun sets.）
　
　 否定句：
　 She didn't arrive until 6 o'clock.
　 她直到6點才到。
　 Don't get off the bus until it has stopped.
　 公共汽車停穩(wěn)后再下車。
　 I didn't manage to do it until you had explained how.　 直到你教我后，我才會做。

1)Until可用于句首，而till通常不用于句首。
　　Until you told me, I had heard nothing of what happened.
　　直到你告訴我以前，出了什么事我一點也不知道?！?
2)Until when 疑問句中，until要放在句首。
　 ---Until when are you staying?　你呆到什么時候？
　 --- Until next Monday.　呆到下周一?！?br>
注意：否定句可用另外兩種句式表示。
(1）Not until …在句首，主句用倒裝。
　　Not until the early years of the 19th century did man know what heat is.
　　直到19 世紀初，人類才知道熱能是什么。
　　Not until I began to work did I realize how much time I had wasted.
　 直到我開始工作，我才認識到了我已蹉跎了幾多歲月。
(2)　It is not until… that…