单选题But for their generous help, the experiment ______ completed so quickly.A shouldn’t beB couldn’t have beenC wasn’tD hadn’t

题目
单选题
But for their generous help, the experiment ______ completed so quickly.
A

shouldn’t be

B

couldn’t have been

C

wasn’t

D

hadn’t

参考答案和解析
正确答案: D
解析:
句意:要不是他们慷慨相助,试验不可能这么快完成。but for要不是…,位于句首句子用虚拟语气。couldn’t have been本不可能实现但却实现了,虚拟语气。