完成时态的用法mary couldn't have received my letter,or she have replied the letter last week.有了具体的last week 为什么还要用完成时态?为什么用couldn't 能直接用 mary haven't received my letter 还有一个句子请帮忙
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完成时态的用法mary couldn't have received my letter,or she have replied the letter last week.有了具体的last week 为什么还要用完成时态?为什么用couldn't 能直接用 mary haven't received my letter 还有一个句子请帮忙
完成时态的用法
mary couldn't have received my letter,or she have replied the letter last week.
有了具体的last week 为什么还要用完成时态?
为什么用couldn't 能直接用 mary haven't received my letter
还有一个句子请帮忙分析一下
nancy is supposed to have finished her chemical experiment at least two weeks ago.
为什么用完成时态
完成时态的用法mary couldn't have received my letter,or she have replied the letter last week.有了具体的last week 为什么还要用完成时态?为什么用couldn't 能直接用 mary haven't received my letter 还有一个句子请帮忙
不是因为有了Last week就是说是过去式.
意思应该是她上个星期已经回了信（她已经回了信,是在上星期）.
couldn't是could not的简写,could表示大概.
意思是说Mary大概还没有收到信,所以加了couldn't表示不确定.
如果去掉couldn't的话就是肯定语气了,语法没错.
两个星期之前nancy就应该应经完成了她的化学实验了,所以是完成时态.
事件到这句话说的两个星期之前已经完成了,而不是2个星期的时候才完成.
receive letter是个持续性的动词，所以用完成时态。
couldn't表示猜测，Mary应该还没收到信，否则她上周就会回复了。如果直接用haven't就表示知道她还没收到，与后半句接不上了。