Describe the commonality between the three variants.
Power plant, avionics, and flight software. One example: Cockpit commonality has a "STOVL/HOOK" button that either lowers the hook on A/C or initiates STOVL flight mode on the B.
(Not to A.A. but to others reading this: Yes, the F-35A has a tail hook, as does the F-15, F-16, and F-22. It is not a carrier capable hook, however.)