If so, she could not have known the answer to his questions.

I don't know the answer to the question which one works best.

He already knew the answer to the question, of course.

We know the answer to the second question quite well.

I do not know the answer to the second question.

No I don't really know the answer to the question.

Both of them already knew the answer to that question.

She did not have to think to know the answer to that question.

My mother doesn't even know the answer to that question.

She didn't want to know the answer to that last question.