Ashtone

If I choose to answer this question at random (with the constraints of having to choose one of the choices) then the chance of it being correct is going to be 25%, because I am answering at RANDOM, therefore not using any intellect and not applying any sense to the question.

However, the question merely states IF you choose, not that you have to.

Therefore, I am entirely correct by answering either A or D.

Thus it is not unanswerable and is incorrect in stating so.