Who said they had to be controlled? Any airfield will do.
Originally Posted by LASORS
a VFR cross-country flight of at least 540km (300 nm) in the course of which full-stop landings at two aerodromes different from the aerodrome of departure shall be made.
So...
A-B-C-A is fine.
A-B-C is also fine, if you don't need to get back to A for some reason.
There is no rule which says you must finish at the airfield you started at.