If you the chat room ten minutes ago, you what we were talking about.
A. have joined; will know
B. would join; have known
C. should join; would know
D. had joined; would have known
网友回答
A. have joined; will know
B. would join; have known
C. should join; would know
(答案→)D. had joined; would have known
解析：考查虚拟语气。句意：如果你十分钟以前加入了聊天室，你就会知道我们正在谈论什么。结合语境可知条件句中是对过去状态的虚拟，故用过去完成时态，主句中用过去将来完成时态，“would+have+done”表示对过去事情的假设，意思是“本来会做”。故选D。