(a) The board shall select as depository for the funds of the corporation a bank in this state that is insured by the Federal Deposit Insurance Corporation and require from the depository a bond in an amount the board finds necessary to protect the corporation.
(b) Funds allocated by the board to a sinking fund for replacement, amortization of debts, and the payment of interest that are not required to be spent in the year in which deposited shall be:
(1) invested in bonds or other evidence of indebtedness of the United States;
(2) placed with the depository in an interest-bearing savings account;
(3) invested in shares or share accounts in a savings and loan association insured by the Federal Deposit Insurance Corporation; or
(4) invested in an investment that is authorized under Subchapter A, Chapter 2256, Government Code, and by a written investment policy approved by the board that complies with Section 2256.005, Government Code.