If the operation __ carefully prepared, it would not have been s

If the operation __ carefully prepared, it would not have been successful.
A、was not
B、has not been
C、had not been
D、were not
【正确答案】：C
【题目解析】：本题考查虚拟语气。主句是对过去的虚拟，所以根据句意，条件状语从句也应该是对过去的虚拟，所以用had done的形式。句意：如果手术没有经过认真仔细的准备，它就不会成功。