问题
选择题
_____ that air conditioners cause so much pollution, I would never have bought one.
A．Had I known
B．I had known
C．Were I to know
D．Did I know
答案
答案：A
考查虚拟语气。根据句意可知考查与过去事实相反的虚拟语气，从句用had + done，Had I known ="If" I had know，故选A。
银汞合金充填体相连接，不能分开，且有悬突，牙龋 * * 红肿，探出血，叩痛(±)，冷(-)