Sec. 5. (a) Every person who is an officer on September 2, 1971, shall become a participant, unless the officer files a written notice of his election not to participate with the board within twenty (20) days prior to September 2, 1971.
(b) Every person who becomes an officer after September 2, 1971 shall become a participant as a condition of his employment.
(c) Any officer who elects not to become a participant shall thereafter be forever ineligible to become a participant.