Не может быть чтобы он не знал как

Не может быть чтобы он не знал как ответить на вопрос: он очевидно очень волновался

Результаты (английский) 1:

May not be that he did not know how to answer the question: it's obviously very worried

Результаты (английский) 2:

It can not be that he did not know how to answer the question: he is obviously very worried

Результаты (английский) 3:

it can't be that he doesn't know how to answer the question, he was obviously very nervous