I would say this is a question of what the BEST answer is for a question. You could use a loop, but then you would need to change the values multiple times in the loop based on the size and location of the circle. For this reason, you would want to use a function.
I think the students' objection is fair, but I always tell students that on many multiple choice tests there maybe a few suitable answers but one BEST answer.
I'd be interested to hear how others deal with this!