about this puter program, a huge amount of time and energy .
A. Should I know; be saved
B. If I had known; can be saved
C. Had I known; would have been saved
D. Did I know; was saved
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A. Should I know; be saved
B. If I had known; can be saved
(答案→)C. Had I known; would have been saved
D. Did I know; was saved
解析：选C。考查倒装句和省略。含有should, had或were的虚拟条件句, 可省略if, 必须将should, had或were提到主语前。此处表示与过去事实相反的假设, 故选C。