SA CIVIL AVIATION REGULATIONS
PART 91: GENERAL AVIATION AND OPERATING FLIGHT RULES
91.03.4 Air traffic service flight plan and associated procedures

(4) The ATS flight plan shall be filed in respect of

(a) all flights to be conducted in controlled or advisory airspace: Provided that this requirement shall not apply in respect of

(i) a local flight;
(ii) a flight crossing an airway or advisory routes at right angles; or
(iii) a VFR flight entering or departing from an aerodrome traffic zone or control zone, from or to an unmanned aerodrome and where no other controlled or advisory airspace will be entered during the flight;

Let's examine the given options:

A flight between two aerodrome traffic zones even though no controlled or advisory airspace will be entered en route. → CORRECT. Flights between controlled aerodromes typically require a flight plan. If one of the two aerodromes is an unmanned (uncontrolled) a flight plan is not required.

Only flights entering Class A or Class C controlled airspace. → INCORRECT. All flights to be conducted in controlled or advisory airspace should file a flight plan. This occurs in airspace class A, B, C, D, and F.

Local flights remaining within the circuit of the departure aerodrome. → INCORRECT. Local flights do not need a flight plan [(a)(i)].

International flights only. → INCORRECT. All flights to be conducted in controlled or advisory airspace should file a flight plan. This might include domestic flights as well.