. If only I how to operate an electronic computer as you do. A. had knownB. would knowC.

问题补充：

. If only I how to operate an electronic computer as you do.

A. had known

B. would know

C. should know

D. knew

答案：

A. had known

B. would know

C. should know

(答案→)D. knew

解析：因为if only (要是…就要了) 其后的句子要用过去式表示虚拟语气，由as you do可知，是与现在事实相反，所以选knew。