If only we then the disease was curable.A. knew B. could know C. had known D. wo

 If only we ____ then the disease was curable.

A. knew B. could know C. had known D. would have known

试题答案

C

解析：if only引导的句子用虚拟语气，表示与过去的事实相反时，动词用过去完成时。