I his telephone number. Had I known it, I would have rung him up.A. don’t knownB. didn’t

网友回答

A. don’t known
(答案→)B. didn’t know
C. hadn’t known
D. haven’t known
解析：    
试题分析:考查动词时态。后句的虚拟语气是对过去的虚拟，由此可知此处是讲述过去的事实，故用一般过去时，答案选B。句意：我不知道他的电话号码。如果我知道的话，我就会给他打电话了。