(a) Except for the original appointments, each commissioner shall serve for a term of two years and until his successor is qualified.
(b) One of the original appointees of the city council and one of the commissioners court shall serve for one year. The other original appointees shall serve for two years.
(c) Each commissioner shall serve his full term unless removed by the authority which appointed him. He may be removed for malfeasance, nonfeasance in office, inefficiency, or other sufficient cause.
(d) If a vacancy occurs through death, resignation, or other reason, the vacancy shall be filled in the manner provided for making the original appointment.