We're fortunate that it didn't rain today.We wouldn't have been able to play golf!
解析; fortunately it didn't rain .没下雨这是事实
If it had rained,we wouldn't have been able to play golf.其实没有下雨,其实打了球,和过去事实相反,所以用了过去完成时,这是虚拟语气.
高考题 I was busy yesterday,or i would have come.昨天忙(事实),否则就来了(其实没有来)
i would have come,but i was busy yesterday.对过去的虚拟用过去完成时