（每当有人打扰他时）
If there was a scarcity of anything，prices of that thing went up．
如果什么物品短缺，那种物品的价格就会上涨。
（d）当if用来表示as或since的时候，主句中可能用各种时态。这里if+过去时态具有过去的含义。这种句子并不是真正的条件句。
—The pills made him dizzy．All the same he bought／has bought／is buy－ing some more．
—If they made him dizzy why did he buy／has he bought／is he buying more？
—那种药使他头晕。尽管如此，他还是又买了一些／又再买了一些／还要再买一些。
—如果那些药使他头晕，那他为什么还买了／买／还准备再买？
—I knew she was short of money．
—If you knew she was short of money you should have lent her some．／why didn’t you lend her some？
—我知道她缺钱。
—如果你知道她缺钱，你应该借给她一些。／你为什么不借给她一些？
2 if从句的各种变化
有时不用if+一般过去时，而可以用下列各种时态：
（a）if+过去进行时
（We’re going by air and）I hate flying．If we were going by boat I’d feel much happier．
（我们准备乘飞机去而）我讨厌乘飞机。要是我们乘船去的话我会感到愉快得多。
If my car was working I would／could drive you to the station．
要不是我的车坏了，我会开车送你去车站的。
（b）if+过去完成时
If he had taken my advice he would have heen a rich man now．
如果他听了我的劝告，他现在会是一个有钱人了。（这是类型2和类型3的混合用法。第223节中将再举一些这种例子。）
（关于if＋would，参见第224节。）
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[Amber demo]
223 条件句类型3
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A if从句中的动词用过去完成时，主句中的动词用条件完成时。这种句子所指的时间是过去；所提出的条件是不可能实现的，因为if从句中的动作在过去并未发生。
If I had known that you were coming I would have met you at the air－port．
要是我早知道你要来的话，我就会在机场接你了。（但我不知道，所以我也没去。）
If he had tried to leave the country he would have been stopped at the frontier．
要是他当时试图离开这个国家，他就会在边界被阻拦。（但他并未这样做。）
B 基本形式可能的变化形式
1 可以用could或might而不用would：
If we had found him earlier we could have saved his life．
要是我们那时早点找到他的话，我们会把他救活的。（能力）
If we had found him earlier we might have saved his life．
要是我们那时早点找到他的话，我们可能会把他救活的。（可能性）
If our documents had been in order we could have left at once．
要是我们的证明文件都齐备的话，我们那时就能够马上走。（能力或允许）
2 可以用条件完成进行时：
At the time of the accident I was sitting in the back of the car，because Tom’s little boy was sitting beside him in front．If Tom’s boy had not been there I would have been sitting in front．
事故发生的时候，我坐在车子的后座，因为汤姆的小儿子坐在前边他的身旁。要是汤姆的孩子没坐在那里的话，我就会坐在前面了。
3 可以在if从句中用过去完成进行时：
I was wearing a seat belt．If I hadn’t been wearing one I’d have been seriously injured．
我当时系了安全带。要是没有系上的话，我就会受重伤了。
4 可以把类型2和类型3结合起来：
The plane I intended to catch crashed and everyone was killed．If I had caught that plane I would be dead now／I would have been killed．
我原想赶乘的那架飞机坠毁了，所有乘客都遇难身亡。要是我赶上了那架飞机，我也就没命了／我就会摔死了。（类型 3）
If I had worked harder at school I would be sitting in a comfortable office now；I wouldn’t be sweeping the streets．
要是在上学时学习再努力一些，我现在就会坐在舒适的办公室里，而
5 had可以位于句首并省略if：
If you had obeyed orders this disaster would not have happened．相当于：
Had you obeyed orders this disaster would not have happened．
要是你当时服从了命令，这场灾难就不会发生了。
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[Amber demo]
224 if从句中的will／would和should
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通常这些助动词不用于条件句中的if之后，然而以下情况例外。
A if you will／would常用于有礼貌的请求中，此时可用更有礼貌的形式would。
If you will／would wait a moment I’ll see if Mr Jones is free．
请您稍候片刻，我看看琼斯先生是否有空。（请等候）
I would be very grateful if you would make the arrangements for me．
如果您能为我安排一下，我将不胜感激。
假如这种要求在当时的情况下通常都会提出，已成为套话，if you would+动词原形就常常单独使用。这表示说话人认为对方理所当然会照办。
If you’d fill up this form．
请填好这张表。
（in a hotel） If you’d just sign the register．
（在旅馆中）请在登记簿上签名。
（in a shop）If you’d put your address on the back of the cheque．
（在商店里）请在支票的背面写下你的地址。
（in a classroom）If you’d open your books．
（在教室里）请打开你们的书。
B 表示愿意的if+will／would适用于所有人称：
If he’ll listen to me I’ll be able to help him．
如果他听我说，我就会帮助他。（如果他乐意听……）
If Tom would tell me what he wants for his dinner I’d cook it for him．
如果汤姆愿意告诉我他晚饭要吃什么，我就会做给他吃。（说话人的意思是说汤姆不愿告诉她。）如在这里使用won’t时，则意味着拒绝：
If he won’ t listen to me I can’t help him．
如果他不肯听我的话，我就不能帮他的忙。