作业帮这里为什么用完成时.the exam must have been very difficult.her husband had been killed in a car crash.完成时我记得是强调对现在或者过去的影响,但是这两个句子里体现不出来啊,帮我分析下这两个句子,
来源：学生作业帮助网 编辑：作业帮 时间：2024/05/05 02:26:13
这里为什么用完成时.the exam must have been very difficult.her husband had been killed in a car crash.完成时我记得是强调对现在或者过去的影响,但是这两个句子里体现不出来啊,帮我分析下这两个句子,
这里为什么用完成时.
the exam must have been very difficult.
her husband had been killed in a car crash.
完成时我记得是强调对现在或者过去的影响,但是这两个句子里体现不出来啊,帮我分析下这两个句子,
这里为什么用完成时.the exam must have been very difficult.her husband had been killed in a car crash.完成时我记得是强调对现在或者过去的影响,但是这两个句子里体现不出来啊,帮我分析下这两个句子,
must have done/been 表示的是对发生在过去的事情的一个 肯定猜测,
比如,他一定是把蛋糕都吃了.He must have finished all of the cakes.
否定猜测是can't have done/been,比如 他不可能把这些蛋糕都吃了 He can't have eaten all of the cakes!
跟这个类似的还有,should (not) have done/been,might (not) have done/been need (not) have done/been,只有must 不能直接说must not have done/been 用can not have done/been
第二句,我回答过其他关于过去完成时的用法,过去完成时有时候特指时间点的位置,表示比过去式早一个点,比如我给你改成," When I broke into the house,her husband had been killed." 当我破门而入了,她丈夫已经被杀了.表示在进去之前就死掉了.有先后顺序.也跟你说的"对过去的影响" 不冲突啊,如果他在我进门后死的,表示我这个警察办事不利,但是我冲进去前就死了,那是没办法的事.
第一个句子是表示对过去事情的非常肯定语气的猜测 must have done
第二个句子是过去完成时 句子应该有一定的语言背景 她的丈夫此前在一场车祸中丧生。并且这个事情对她过去（她丈夫死后）的生活有所影响。
must+have done表示对过去的情况进行推测，第一句the exam must have been very difficult.就属于这种而过情况。
must+have done也强调强调动作的完成，第二句her husband had been killed in a car crash属于这种情况。
希望能帮到您。。望采纳
must have been不全部是完成时，它是对过去情况的推测。再给你举例： A It must have rained last night, for it is wet on the ground.过去时 B. He must have already been to Japan, for he knows a lot a...
全部展开
must have been不全部是完成时，它是对过去情况的推测。再给你举例： A It must have rained last night, for it is wet on the ground.过去时 B. He must have already been to Japan, for he knows a lot about Japan.完成时 你的句子属于这一类。 如没有具体的语境，单凭这一句是错误的。
收起
第一句是must have been结构，表示肯定的有把握的猜测；
第二句是陈述已发生的事实，到目前为止她丈夫已经被车撞了。