(a) Each director shall serve a term of four years.
(b) Notwithstanding subdivision (a), the directors initially appointed to the board shall determine, by lot, that one-half plus one of their number shall serve for four years and the remaining directors shall serve for two years. Thereafter, each appointing authority shall appoint a person to replace its respective director or may reappoint its director for an unlimited number of terms.
(c) A vacancy on the board shall be filled by the respective appointing authority not later than 90 days from the date of the occurrence of the vacancy.