The retirement benefits program of the District shall consist of:
(1) A defined benefit plan, as provided in 42 U.S.C. § 301 et seq. (“Social Security Act”);
(2) An employee deferred compensation plan pursuant to § 457 of the Internal Revenue Code [26 U.S.C. § 457] governed by Chapter 36 of Title 47; and
(3) A defined contribution plan pursuant to § 401(a) of the Internal Revenue Code [26 U.S.C. § 401].