请问这道虚拟语气的英语选择题怎么做？

Question

Had I known about this computer program,a huge amount of time and energy_____.
A.would have been saved B.had been saved C.will be saved D.was saved
请说一下理由？

Answer 1

Had I known about this computer program,a huge amount of time and energy_____.
A.would have been saved B.had been saved C.will be saved D.was saved
请说一下理由？
答：A
译：要是我当时了解这个计算机程序的话，就会省掉大量的时间和精力了。
析：虚拟语气，虚拟过去，倒装省略if的用法。
我们知道，与过去事实相反的假设，虚拟条件句用if 主+had done sth, 主句用would +have done sth. , 从句中如有助动词had,(should, were),可能通过提前而省略if,所以，Had I known ...= If I had known ...,.....

Answer 2

选A，
主句为过去完成时（If I had known....）,从句用过去将来完成时（would have done）

Answer 3

选A，
从句属于倒装，将had提前，还原就是If I had known about...，根据had done（过去完成时）可判断是在过去时的基础上往前推一个时态，也就是对过去虚拟，所以主句应用would/should/might have done 的结构，即A。

Answer 4

选择A。解析：这是虚拟语气中的一种。从句是had+过去分词，那么从句则要用would+have+过去分词，又因为时间和精力是被节省，所以要用被动语态。整句话的意思是：假如我知道这个电脑程序，那么将会节省许多时间和精力。

Answer 5

表示对过去的虚拟，从句过去完成时had done，主句would /should/could/might have done

Answer 6

此题正确答案为选项A。理由如下：
题干中逗号前面的分句是一个省略了if的虚拟条件句（用倒装语序），从其谓语动词形式“had known"可知为过去完成时，因此可以判断出这是一个和过去事实相反的虚拟条件句。在这种情况下，主句的谓语动词形式为：would/could/should/might have +动词的过去分词。故本题的正确答案为选项A。
全句可译成汉语：如果我（当时）了解这种电脑程序，就会省去大量的时间和精力了。
又如：
If I had seen your question earlier (or: had I seen your question earlier), I would have answered it. 如果我早点儿见到你的问题，我可能已经回答了。
希望我的回答对你有所帮助！