问题补充:
If you had joined the chat room ten minutes ago, you what we were talking about.
A. would know
B. would have known
C. knew
D. had known
答案:
A. would know
(答案→)B. would have known
C. knew
D. had known
解析:考查虚拟语气。句意“would+have+done”表示对过去事情的假设,意思是“本来会做”。如果你十分钟前加入聊天室,你就会知道我们正在谈论什么了。“would+have+done”表示对过去事情的假设,意思是“本来会做”。故选B。