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问题: 怎么判断这是一个省去了IF的条件状语从句:What would have happened had Bob walked farther?

解答:

很简单,条件状语从句中的IF一旦省略,句子必须到装,也就是说要将句子的谓语动词提前,What would have happened had Bob walked farther?这句话也可以这样表达:Had Bob walked farther, what would have happened?前句的主语即为后句的主语.此处的虚拟语气也是有规可循的,如果前句用过去完成时态,那么后句就必用would/should/could+have+过去分词结构,如果前句用过去时,那么后局就用过去完成时态或would/should/could+动词原形来表示.其他我就不一一说了,你自己可以看语法书来进行总结.