I'm confused about a multiple-choice question:
The boy insisted that he __________ the glass. He said that he was not there then.
a. hadn't broken
b. didn't break
c. haven't broken
d. not break
The correct answer is a, while I would choose b if it was necessary to express the same meaning as the exercise sentence. Meanwhile, a seems correct to me as well, which I guess can be based on an explanation that the action "not break" happened before the moment "then". Therefore, could anybody show me the conventional way to make up this sentence? Can it be "The boy insisted that he didn't..." or "The boy insisted that he hadn't...", or both sound familiar to native speakers?