ENR 1.1 10.2 Except when identified, position reports are required for all aircraft in classes A, C and D airspace, and for IFR flights or flights using the IFR Pick-up procedure after initial contact with ATC in classes
E and G airspace.
Wilcome maybe this can clarify why you had trouble with this question as reporting has nothing to do with CTA vs OCTA rather whether you are RADAR identified or not. As said before a thorough understanding is required to pass irex well and it rates up there with some ATPL exams in difficulty.