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3．in case引导从句的区别 in case既可引导目的状语从句，也可引导条件状语从句，主要视句意而定： In case he comes, let me know.(条件状语从句) 如果他来，告诉我一声。 Tell me in case you get into difficulty.(目的状语从句) 遇到困难请告诉我。 in case引导目的状语从句，从句有时可用“should＋动词原形”这样的形式： Take your coat in case it rains (should rain)． 带着雨衣以防下雨。 五、条件状语从句 1．引导条件状语从句的从属连词 (1)主要的有if, unless, as (so) long as等。 You can leave now if you like. 如果你愿意现在就可以走了。 As long as it doesn't rain we can go. 只要不下雨，我们就可以去。 (2)除以上基本的引导条件状语从句的从属连词外，还有的动词尤其是其分词形式(如suppose, supposing, provided, providing等)和介词短语(如in case, on condition that等)也可用作连词表示条件。 I will come on condition (that) she is invited too. 如果邀请她来， 那我就来。 He may go with us provided (providing) he arrives in time. 他若及时到，就可以和我们一起走。 suppose和supposing引导条件状语从句时，通常用于主句为疑问句的场合： Suppose the boss saw you，what would he say? 如果老板看到你，他会怎样说？ Supposing he does not come, shall we go without him? 他若不来，是不是不带他去？ 2．条件状语从句的时态 当主句为将来时态或具有将来意义时，条件状语从句通常要用一般现在时表示将来意义，而不能直接使用将来时态。 六、时间状语从句(两个方面) 1．引导时间状语从句的从属连词 引导时间状语从句的从属连词很多，如较基本的有before, after, when, while, as, since, till, until, as soon as 等。 Things were different when I was a child. 我小时候情况与现在不同。 We must strike while the iron is hot. 我们要趁热打铁。 It's a long time since I met you last. 从上次见到你，已有很长时间了。 除以上基本的引导时间状语从句的从属连词外，还有些本来不是从属连词却可用作从属连词的词： | 
