They must have arrived by now,haven't they?为什么用haven't they?不用didn't they?by now 布什表示过去发生的吗

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They must have arrived by now,haven't they?为什么用haven't they?不用didn't they?by now 布什表示过去发生的吗

They must have arrived by now,haven't they?为什么用haven't they?不用didn't they?by now 布什表示过去发生的吗
They must have arrived by now,haven't they?
为什么用haven't they?不用didn't they?
by now 布什表示过去发生的吗

They must have arrived by now,haven't they?为什么用haven't they?不用didn't they?by now 布什表示过去发生的吗
因为They must have arrived by now中动词是 HAVE
所以用haven't 作反问
by now 表示至今

by now是在现在,
他们在这个时候应该已经到了,不是吗?
前后时态要一致。

by now 是到现在为止,因为前面是have arrived,所以前后要统一

这是虚拟语气.具体情况具体分析.
本句中是推测他们一定会到,而他们此时还没到.这时用虚拟语气.具体请参考语法书这一章内容

因为前面用的是 have ,所以前后对应

这是一句反义疑问句,问句中的助词是HAVE所以,后面也一样,是与主句呼应.