For example, an estimate would be appropriate if you're having a casual birthday party and want to know roughly how many bags of chips you should buy.
请问老师:
1 if条件句是使用了虚拟语气吗?不懂主句和if从句所使用的时态是如何选择的?根据什么来决定呢?
2 if从句中还使用了两种不一样的时态,为什么呢?
这里的 if you're having a casual birthday party and want to know roughly how many bags of chips you should buy 是真实条件句,不是虚拟条件句,所以谓语动词没有使用虚拟语气。