But let me know if I didn't understand the question.

Some were so far gone they didn't even seem to understand the question.

No one else would have been able to understand his question.

For a moment, I thought he didn't understand the question.

For a moment it seemed as if she didn't understand the question.

I did not understand quite well your question and may be you could bring more light on it.

That was his stock answer when he didn't understand the question.

At first I didn't understand her question and couldn't talk anyway.

But quite often they have not really understood the question.

The older man seemed to understand the other's mental question.