(a) The proceeds from the sale of any issue of bonds may, within the discretion of the board, be invested prior to their use for the purposes for which they were issued, in bonds or other direct obligations of, or obligations unconditionally guaranteed by, the United States or in certificates of deposit issued by banks as long as the certificates are secured by such obligations or may be invested in accordance with Subchapter A, Chapter 2256, Government Code.
(b) The investments may be sold pursuant to the directions of the governing body as and when needed for their use for the purposes for which the bonds were issued.