急！英语问题！！！

Question

请问一下，Sam was sure that the wallet must have been found by one of the villagers, but it was not returned to him.这句话可不可以改成Sam was sure that the wallet must had been found by one of the villagers, but it was not returned to him.这样？这里为什么不用过去完成式呢？为什么不能用had been found呢？

对不起我是新手，初始分只有20，还被抵押了5分..= =..这是我所有的分了。。求好心人解答

Answer 1

你的意思是把原句中的have换成had？
这是不可以的
因为在must后面要用动词原形，即使是助动词也要满足。
过去完成时要表示过去的过去发生的动作或者状态对过去造成的影响或者结果。比较容易的区分方法就是要有比较明确的时间状语。这里其实可能已经是过去的完成时了，只是没有体现在have/had 上面，毕竟must的分词形式和原形是一样的追问

谢谢你回答的这麼详细，很感动，我也很想把分给你，要是分能分成好几份就好了。。

Answer 2

没看懂你的问题是什么意思。
Sam was sure that the wallet must had been found by one of the villagers, but it was not returned to him.这句话是正确的。

Sam was sure that the wallet must have been found by one of the villagers, but it was not returned to him。这句话是个病句。追问

谢谢你的回答，可这是新概念第二册上的原句，怎么会是病句呢？我确定没有写错喔，Lesson 45:clear conscience 这篇课文里的

追答

我看错了，漏看了must。

不能改。因为must 后面 跟动词原型，所以只能是have。

追问

追答

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Answer 3

因为是was not returned.，用现完