pleace they must have finished their work by now.为什么用have finished?they finally succeeded in carrying out the experiment.they must have finished their work by now.为什么用have finished?i have been looking forward to hearing from you.为

pleace they must have finished their work by now.为什么用have finished?they finally succeeded in carrying out the experiment.they must have finished their work by now.为什么用have finished?i have been looking forward to hearing from you.为
pleace they must have finished their work by now.为什么用have finished?
they finally succeeded in carrying out the experiment.
they must have finished their work by now.为什么用have finished?
i have been looking forward to hearing from you.为什么用have been?
it has not been decided yet when the meeting will start at the hall.为什么用been,不要be?
i won't visit that restaurant today.won't 在什么时候用?

pleace they must have finished their work by now.为什么用have finished?they finally succeeded in carrying out the experiment.they must have finished their work by now.为什么用have finished?i have been looking forward to hearing from you.为
1.通过后面的 BY NOW 我们可以了解到 主人翁肯定已经做过这件事 所以用MUST HAVE DONE 来说明非常确定 .翻译：他们现在肯定已经完成他们的工作了.
2.他们最终成功地完成了那项实验.
3.现在完成时 有一条 叫做 如果句子中的动作从现在开始并对以后有所影响 将需用现在完成时 这里就是 我很期待收到你的来信.即是这种情况.
4.这是毫无疑问的啊 前面用了has 后面如果再用BE 的话 一句话不就出了两个谓语了吗 而且 由翻译也可得出 这句话需用现在完成时 而现在完成时的基本结构不就是 something has (not ) been done
翻译：到底什么时候会议会在大厅开始到现在还没确定下来.
5.won't 是will not 的缩写形式 一般情况下 是用于一般将来时的 有时在虚拟语气中也可能会用到 要是情况而定了 .和WILL 用法一致 是WILL 的否定形式了 .
个人分析的 很辛苦 真心希望能帮到楼主

1、他们最终实施出了那个实验。
2、by加一段时间“到`````为止”是完成时的标志：现在他们肯定完成了他们的工作，强调对现在造成的影响，因此用have finished.
3,、这里用的是完成时，“会议什么时候将会在大厅召开还没有决定”has been decided 是完成时的被动形式，be 只能是一般现在时的被动，因此不用。
4、“我不打算今天参观哪个旅馆”参观这个动...

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1、他们最终实施出了那个实验。
2、by加一段时间“到`````为止”是完成时的标志：现在他们肯定完成了他们的工作，强调对现在造成的影响，因此用have finished.
3,、这里用的是完成时，“会议什么时候将会在大厅召开还没有决定”has been decided 是完成时的被动形式，be 只能是一般现在时的被动，因此不用。
4、“我不打算今天参观哪个旅馆”参观这个动作并没有发生，虽然没有明确的时间状语，仍应该用将来时表示，won't只是will的否定形式，和will的用法是没有区别的。

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他们最后成功完成了实验。
因为后面有by now 完成时，可看语法关键词。
持续期待，现在完成进行时
前面是have 要加been
表将来某一时间。