这一道英语题为什么这么选择？？？15

这是个“省略加提前”的虚拟条件句，把这个句子还原成我们熟悉的就是：

If they were to arrive before we depart the day after tomorrow, we should have a wonderful dinner party.

具体语法如下：

在虚拟条件句中，有时可将虚拟条件句的连词if省略，但此时应用倒装句型，即将从句中的were, should, had 等提到句首。如：
如果她在这里，她也同意的。
If he were here, she would agree too.
→Were she here, she would agree too.
假若明天下雨，我们只好推迟这场比赛。
If it should rain tomorrow, we should have to put off the match.
→Should it rain tomorrow, we should have to put off the match.
要是我们当时早点找到他的话，我们就可以救活他。
If we had found him earlier we could have saved his life.
→Had we found him earlier we could have saved his life.

具体分析：

1. 排除B，就没有这种形式

2. be to do 表示即将发生的事，也就是一种将来时态，因为句子里讲的是后天的情况，所以要用将来时态 be to do，这样A.C都不对。

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首先要知道if引导的虚拟句型
对过去的虚拟：从句 if + had done（过去完成） 主句 would/could/should/might + have done（现在完成）
对现在的虚拟：从句 if + did（过去式） 主句 would/could/should/might + do（动词原型）
对将来的虚拟：从句1) if + should + do（动词原型）;
2) if + were to +do（动词原型）;
3) if + did（过去式）; 主句 would/could/should/might + do（动词原型）
在此题中 the day after tomorrow是表示对将来的虚拟， A 选项 have done 是对过去的虚拟
所以应该是 if they were to arrive before the day after tomorrow
另外if条件句中如有were, should, had，可以省去if，并使用倒装语序,所以应该选D

虚拟语态，如果后天在我们离开前他们到这.....

D对，虚拟将来式。

我觉得该选A啊