Hi William,
One reason why your query did not get answers so far is that it is hard to understand why you would want this behavior. If "not applicable" is a correct answer, then it should count as such, no? Or, to put it another way, if your wish was possible, then if the people taking your quiz see a
MCQ question with one of the choices labeled "not applicable" they would simply skip it, in order to not be penalize for a wrong answer.
I'm finding it hard to imagine exactly why you would want that "not applicable" option anyway. Could you provide a real-world example, please?
Joseph