He lost his left leg.If I ( )more about going first aid,Icould have helped.A.knew B.have known C.had known D.would know说明原因

He lost his left leg.If I ( )more about going first aid,Icould have helped.A.knew B.have known C.had known D.would know说明原因
He lost his left leg.If I ( )more about going first aid,Icould have helped.
A.knew B.have known C.had known D.would know
说明原因

He lost his left leg.If I ( )more about going first aid,Icould have helped.A.knew B.have known C.had known D.would know说明原因
答案选C.had known
这是if 引导的与过去事实相反的虚拟语气用法
翻译：他失去了它的左腿.如果我能多了解一些急救知识,就可能会帮到他了.

C. had know
if引导(与过去事实相反)的虚拟语气
他失去了它的左腿。如果我能多了解一些急救知识，可能帮到他。（事实上没帮到）