they failed to finish the project in time.i regretted______them.

题目

they failed to finish the project in time.i regretted______them.
A to be not able to help B being not able to help C not being able to help
D not be able to help
为什么不是其它选项呢

答案

C
首先 regret doing "遗憾做了某事" 跟现在分词,跟动词不定式是"还没做什么表示遗憾" 句意是:他们没有按时完成项目,我非常遗憾没能帮上他们的忙.
现在分词的否定形式 not doing
所以选C
比较:
Regret to do sth 后悔,遗憾要做什么事(但还没做)
Regret doing sth 后悔,遗憾做过什么事
例句:
I regret to have to do this,but I have no choice.
我很遗憾必须这样去做,但我实在没有办法.
I don't regret telling her what I thought.
我不后悔没把我的想法告诉她.