请问这道题考察的什么知识点？请给我讲讲吧

来源：百度知道 编辑：UC知道 时间：2024/05/22 03:24:04
＿＿for your help,I'd never have been able to get over the difficulties.
A.Were it not B.Had it not been C.If it were not D.If it had been

B
If 引导的虚拟语气，If在前句首倒装
与过去事实相反，从句用过去完成时

选A.Were it not
虚拟语气表如果没有发生什么什么,就不会怎样怎样..
常用于假设的情形和结果与事实正好相反.