__before we leave the day after tomorrow,we should have a wonderful party

答案是were they to arrive 还有 Had they arrived Were they arriving Would they arrive
一点这个倒装句的助词提前为什么是were是过去式 ，不是原形are 不是had或 did
二点 to arrive arrived ariving arrive分别在什么情况下用

were they to arrive 在这里是虚拟条件句，从时间状语the day after tomorrow（后天）来看 是对将来的虚拟， 所以选这个
它等于If they were to arrive...

Had they arrived 是对过去的虚拟， 等于 if they had arrived, 与语境不符

没有这两种 虚拟形式（Were they arriving 和 Would they arrive）

如不明白请追问，如果满意请采纳
手机提问者如果满意，请在客户端右上角评价点“满意”即可， 谢谢！

祝学习进步

leave和should have这两个动作以及the day after tomorrow这个时间都告诉我们，这是还未发生的事。要用一般将来时的虚拟语气：were to do sth. a项是一般过去时的虚拟语气。 祝你学习进步，更上一层楼！ (*^__^*) 不明白的再问哟！请记得采纳，多谢！