Question

____before we leave the day after tomorrow, we shold have a wonderful dinner party .

a were they to arrive b would they arrive
why　no　choice b？

Answer 1

这是将来时的虚拟语气，固定结构为：从句谓语部分用“were to/should+动词原形”，主句谓语部分用“would/should/could/might+动词原形”。
该句子只是一般将来时的虚拟语气的一般疑问句形式。
因为“____before we leave the day after tomorrow”为从句，所以用“were to/should+动词原形”，故选择a.
如果将b选项中的would改为should，那么该答案也是正确的。

对你有所帮助的话，请及时采纳喔~~

Answer 2

这是一个虚似条件问，因此可以确定用would，用were显然不行的。可以排除A。

因为条件句中省略了if，因此整句要倒装，把would提前，would they arrive。

if they would arrive before we leave the day after tomorrow, we shold have a wonderful dinner party .

这样看就会好理解了。

追问

应该是考察虚拟语气吧，与现在事实相反 用WERE加动原，不过谢谢了，你提醒了我是考察这个语法