Which preposition to use with exam

in Occurrences 1%

" "Tutor this summer and have another go at those exams in September.

of Occurrences 1%

So off went J.W. with his armful, and for a week thereafter you might have supposed he was cramming for a final exam of some sort.

on Occurrences 1%

Why, I could pass their exams on my head, if I hadn't anything better to do.

Which preposition to use with  exam