All municipal bonds, revenue bonds, or other investments of monies of the Bank provided for under this chapter must at all times be purchased in negotiable form, subject to provision for any registration in the name of the Bank or for issuance in book entry form pursuant to section 1881 of this title. All municipal bonds and revenue bonds at any time purchased by the Bank must upon delivery to the Bank be accompanied by an approving opinion of bond counsel. (Added 1969, No. 216 (Adj. Sess.), § 3, eff. March 27, 1970; amended 1971, No. 148 (Adj. Sess.), § 6, eff. Feb. 14, 1972; 1987, No. 55, § 19, eff. May 15, 1987.)