The agreement entered into, pursuant to Section 40321, shall provide one of the following alternatives:
(a)
The number of supervisors, and the number of members of the city selection committee, appointed by their respective bodies, from each county included, in whole or in part, within the regional district to be members of the regional district board.
(b)
The weight of vote of each member of the regional district board if each board of supervisors and city selection committee of such counties are represented on the regional district board by the same number of members thereof.
(c)
A combination of subdivisions (a) and (b).
The agreement shall also provide a procedure for its modification or termination.