The commission shall be:
(1) elected at large;
(2) elected by districts in which candidates must reside and which are apportioned by population;
(3) elected at large and nominated by a plan of nomination that may not preclude the possibility of the majority of the electors nominating candidates for the majority of the seats on the commission from persons residing in the district or districts where the majority of the electors reside; or
(4) elected by any combination of districts, in which candidates must reside and which are apportioned by population, and at large.