[qb45]

I think (a) may be the undergrad student - still young and idealistic :)

Then (b) could be the PhD student who talked to enough people to be aware that you never know what others consider a ball.

Finally, (c) goes to computer because it's the longest one and it's full of Greek letters. I've known a PhD who believed only in proofs starting with "For arbitrary ε > 0, take δ = ...", but even he wasn't as boring as (c).