条件状语从句用法说明条件状语从句主要由if, unless, as [so] long as, in case 等引导。如：一、由if引导Don’t be anxious if I’m late. 如果我来迟了，不要着急。I’ll fire if you come any nearer. 再走近一点我就开枪了。Could you endure poverty if I went away? 我要是离开了你能忍受贫穷吗？You can ask my mother if you don’ t believe me. 你如果不相信我可以问我母亲。If anyone calls tell them I’m not at home. 要是有人打电话来，就说我不在家。You could get a better job if you spoke a foreign language. 如果你能讲外语，你可以找到好点的工作。二、由unless引导You will fail unless you work hard. 你若不努力就会失败。I won’t write unless he writes first. 如果他不先写信，我也不写。Don’t come unless I telephone. 除非我给你打电话否则不要来。We’ll have the outing tomorrow unless it rains. 我们明天去郊游除非是下雨。Unless you wear boots you may be bitted by snakes. 若不穿靴子你可能被蛇咬。I shouldn’t dream of going unless you wanted rIIe. 除非要我去，否则我不会想去。Unless I parted from Sheila, l could not keep up that struggle. 如果我不和希拉分手我就没法坚持这一斗争。三、由as [so] long as引导As long as you need me, I’ll stay. 只要你需要我，我就留下。I’m happy as long as you are happy. 只要你快乐我就快乐。I shall love you as long as I have breath. 只要我还有一口气，我就会爱你。So long as you make Ruth happy I’m content. 只要你让鲁思高兴我就满意了。So long as you make Ruth happy I’m content. 只要你让鲁思幸福我就满足了。You can take my cal so long as you drive carefully. 只要你开车小心，我可以把车借给你。 As long as you understand, we shall say no more about it. 只要你能理解，我们就不说什么了。You may use the room so long as you keep it clean. 你可以使用这个房间，只要你能保持干净。四、由in case 引导In case I forget, please remind me about it. 万一我忘记，请提醒我一下。In case he arrives before I get back, please ask him to wait. 如果他在我回来以前到，请让他等等我。【注】在条件状语从句中，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。不过，有时表示条件的 if之后可能用 will，但那不是将来时态, 而是表示意愿或委婉的请求(will为情态动词)。如：If you will wait a moment, I’ll fetch the money. 请等一下，我就去拿钱。

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