各结构的被动形式
　　<例句>
　　How could he be persuaded to stay?
　　怎么能劝说他留下?
　　<语句分析>
　　由can, could和be可构成被动结构，can, could 后的不定式可用完成形式，may，might或should等词后的不定式也可用完成形式。有一些不定式结构如ought to, be going to等也可构成被动形式。有些成语动词如及物动词+副词，动词+介词，动词+副词(名词)+介词等都可以有被动结构形式。
　　<触类旁通>
　　(1) This can't have been done by a human being.
　　这不可能是人做的事情。
　　语法分析：can, could后的不定式可用完成形式。
　　(2) The road may be further widened.
　　这条路还可再拓宽一点。
　　语法分析：may, might可构成被动结构。
　　(3) They might have been put in the wrong place.
　　它们可能被放错了地方。
　　语法分析：may, might后的不定式也可用完成形式。
　　(4) This ought to be done right away.
　　这事情应当马上去做。
　　语法分析：ought to 的被动结构。
　　(5) When is the dam going to be completed?
　　水坝什么时候建成?
　　语法分析：be going to 构成的被动结构。
　　(6) Her illness was brought on by her worries.
　　她忧虑成疾。
　　语法分析：成语动词的被动结构。
　　(7) We were assigned a lot of homework.
　　我们有很多家庭作业。
　　语法分析：双宾动词的被动结构。
　　<巩固练习>
　　(1) This can't _____ done in a short time.
　　(2) She might _____ sent to work abroad.
　　(3) All these factors mustn't _____ neglected.
　　(4) This should _____ kept a secret.
　　(5) Does this need _____[be] mentioned?
　　(6) How many people are going to _____[send] there?
　　(7) This has to _____[do] promptly.
　　(8) Not a soul was _____[see].
　　(9) You are requested _____[present] at the ceremony.
　　<参考答案>
　　(1) be (2) be (3) be (4) be (5) to be (6) be sent (7) be done (8) to be seen (9) to be present

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