Section 18. Except as otherwise provided in paragraph (c) of section seventeen, or as provided in any bond resolution applicable to any bonds of the Authority, the Authority may invest any funds in (i) direct general obligations of the United States of America, (ii) obligations the payment of the principal and interest on which, by Act of the Congress of the United States or in the opinion of the Attorney General of the United States in office at the time such obligations were issued, are unconditionally guaranteed by the United States of America, (iii) bonds, debentures, participation certificates, notes or similar evidences of indebtedness payable in cash issued by any one or a combination of any of the following: Federal Banks for Cooperatives, Federal Land Banks, Federal Home Loan Banks, Federal Farm Credit Banks, Federal Intermediate Credit Banks, Export-Import Banks of the United States, Farmers Home Administration, Federal Home Loan Mortgage Corporation, Federal National Mortgage Association or Government National Mortgage Association, and the Student Loan Marketing Association, (iv) public housing bonds issued by public agencies or municipalities are fully secured as to the payment of both principal and interest by a pledge of annual contributions under an annual contributions contract or contracts with the United States of America; or temporary notes, preliminary notes or project notes issued by public agencies or municipalities, in each case fully secured as to the payment of both principal and interest by a requisition or payment agreement with the United States of America, (v) direct and general obligations of any state or political subdivision thereof or territory of the United States to the payment of the principal of and interest on which the full faith and credit of such state is pledged, provided that at the time of their purchase such obligations are rated in one of the four highest rating categories by any nationally recognized rating agency, (vi) bank time deposits evidenced by certificates of deposit of or time deposits constituting direct obligations of banks which are members of the Federal Deposit Insurance Corporation or the Federal Savings and Loan Insurance Corporation, provided that, to the extent such time deposits exceed available federal deposit insurance, such time deposits are fully secured by obligations described in items (i) through (iv) above, which at all times have a market value (exclusive of accrued interest) at least equal to such bank time deposits so secured, including interest, or such deposits are due within one year and are issued by banks the senior long-term debt securities of which are rated in one of the four highest categories by any nationally recognized rating agency, (vii) repurchase agreements for obligations of the type specified in clauses (i) through (iv) above with federally insured banking institutions which have a capital and surplus aggregating at least one hundred million dollars, provided such repurchase agreements are fully collateralized and secured by such obligations having a market value, exclusive of accrued interest, at least equal to the purchase price of such repurchase agreements and which shall be delivered to a trustee, (viii) investment agreements with banks the senior long-term debt securities of which are rated in one of the four highest categories by any nationally recognized rating agency and which have a capital and surplus aggregating at least one hundred million dollars, and (ix) in any other manner specifically approved for the purpose of the particular investment by resolution of the Authority. Any such securities may be purchased at the offering or market price thereof at the time of such purchase. All such securities so purchased shall mature or be redeemable on a date or dates prior to the time when, in the judgment of the Authority, the funds so invested will be required for expenditure. The express judgment of the Authority as to the time when any funds shall be required for expenditure or be redeemable is final and conclusive.