（a）She slept till (until) nine.
(b) She didn't sleep till (until) nine.
句(a)与句(b)中的till(until)的含义是否相同?
可以这样来概括 till(until) 的含义: 介词 till(until) 用在肯定句中时通常表示动作的终点, 用在否定句中时则表示动作的起点。
She slept till(until) nine. = She stopped sleeping at nine. 她一直睡到九点钟。
She didn't sleep till (until) nine. = She started sleeping at nine. 她九点钟才开始睡觉。
请分析下列各例中的 till(until) 的含义：
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They talked till dawn. (Palmer) 他们一直谈到天亮。
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She will be working till nine o'clock. 她将一直工作到九点。
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I sometimes stay in bed until lunch time. (NCE 2) 有时我在床上一直躺到吃午饭的时候。
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He's only staying until tomorrow evening. (Mansfield) 他只停留到明天晚上。
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They did not get to bed until late that night. (J. K. Rowling, Harry Potter and the Deathly Hallows) 他们直到夜深了才上床睡觉。(《哈利·波特与死亡圣徒》)
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I didn't know till now that you were ill. (Chambers) 直到现在我才知道你病了。
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Until now I knew nothing about it. (ALD) 直到现在我才知道这件事(在此之前我对此事一无所知)。