The fire service began to wonder whether a gas might have caused the fire.
上句中的 might have caused 能否改为 may have caused?
当站在“现在”的立场来谈论“过去可能发生了某事”时, may have done 与 might have done 是可以互换的:
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He may/might have missed the train. 他可能没有赶上火车。
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The doctor said, "You may have hurt a bone in your back." 医生说: “你后背有一根骨头可能受了伤。”
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You may have noticed some birds sitting on the backs of sheep. (全国高考,96-阅C)你可能看到过某些鸟站在羊背上。
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You might both have been caught and killed! 你们俩可能被捉住砍头的呀！
但是，当站在“过去”的立场来谈论“此前可能发生了某事”时，则只能用 might have done，故你提出的句子中的 might have caused 是不能改为 may have caused 的。
请做下面的英语试题：
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Liza did not come for the piano lesson yesterday. She ____ have missed the bus. A. would B. might C. should D. ought to (全国成人高考,93-26)
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You shouldn't have run across the road without looking round. You ____ by a car. A. should have been knocked off B. may be knocked down C. will have been knocked down D. might have been knocked down