The millions of calculations involved, had they been done by hand, ______ all practical value

Question

The millions of calculations involved, had they been done by hand, ______ all practical value by the time they were finished.

A) had lost B) would lose C) would have lost D) should have lost

我知道正确答案是C，可是想知道为什么不能选D，老师给的复习资料里if表将来的虚拟语气的主句可以用would/should/might/could+have done,为什么这里would行，should就不行呢

Answer 1

第一，这里是表达对过去的虚拟。
第二，should have done 表示本应该。 would have done 表示本会。意思不一样的

Answer 2

would比should的语气要委婉，should的语气过于肯定，所以在两个里选c更合适本回答被提问者和网友采纳