题目内容：

We__the work on time without your timely help.( )
A.had't had finished B.didn't have finished
C.can't have finished D.couldn't have finished
C,D同样是对过去的否定判断,句子中没有时态应该选C,为什么答案是D?请说明一下原因,

优质解答

这个句子用了虚拟语气--加入没有你的及时帮助,我们就不能按时完成那份工作了.
虚拟语气是由should could might were was 等构成,不可以用can shall 等原型形式的.
你也说了是对过去的否定判断,不错,所以应该选D.