It would have been great if we had been able to bottle the smells. It would be a great business if you could do that. 两句都是使用虚拟语气的句子, 为什么第一句 if 后面的从句用过去完成时, 第二句的 if 后面用过去式的could? 它们是不是根据主句的时态而使用的? 能详细解释一下吗?