Mathematical paradoxes and the exam

Not so long ago on Habré was published an article discussing the issue of the exam on programming. And there was a heated discussion on the adequacy of specific test options and the possibility of using testing to assess knowledge in general.

In this regard, I remembered similar discussions about tests in mathematics and the amusing problem connected with it.

Vasya and Petya somewhere produced a watermelon (we consider watermelon an ideal ball of a single volume) and cut it into 20 pieces - possibly unequal. Tanya begged them to give her one part (at her choice) and Vasya agreed to take only 9 parts for herself, and give the rest to Petya. What is the maximum volume Vasya can guarantee himself with a successful cut?
A) not more than 0.8; B) not more than 0.9; C) not more than 1.0; D) more than 1.0

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It is easy to guess the "answer in the exam style" - B. But the correct mathematical answer is even D! Accordingly questions:
1) Is the person who gave the answer D to the USE adequate?
2) Do you want to work with him on the same team?
3) Can you suggest a wording change that would make the correct answer B - and is it wise to change the wording like that?

Fix It seems I did not quite understand. I just never demand that the student know how to give an answer D. On the contrary - I think that in this task only B was considered the correct option - and if some amateur "show off" as a result flies past the university and goes to the wipers - everyone will only get better. Just as in the previous case, I considered it unwise to accept the answer 119bit. Shybko is an intelligent specialist without knowledge of when and where to apply them - “monkey with a grenade” ... Personally, I don’t need this in a team and I’m wondering if anyone else needs it ...