If I about this puter program, a hage amount of time and energy would have been saved.
A. know
B. knew
C. had known
D. have known
网友回答
A. know
B. knew
(答案→)C. had known
D. have known
解析：考查虚拟语气：句意：如果我知道这电脑程序，大量的时间和精力就会被节省下来，从句意和主句的would have done可知是和过去相反的虚拟语气，if条件句用过去完成时，选C。