An insurer may invest in obligations issued, assumed, or guaranteed by the United States, an agency or instrumentality of the United States, a state, a municipality, a political subdivision, the government of Canada, an agency or instrumentality of the government of Canada, any province or municipality of Canada, or any municipal utility, corporate authority, nonprofit corporation, or institution authorized or established by an act of Congress or by the laws of any state, Canada, or any province of Canada if, by statutory or other legal requirements applicable to those obligations, they are payable as to both principal and interest:
(1) From taxes levied or required to be levied upon all taxable property or all taxable income within the jurisdiction of the borrowing entity;
(2) From adequate special revenue pledged or otherwise appropriated or required by law to be provided for the purpose of the payment, excluding any obligation payable solely out of special assessments on properties benefited by local improvements;
(3) From and secured by a pledge of rentals from leases or subleases on property owned or leased by the obligor if: (a) Such underlying lease has an unexpired term of not less than the term of the lease or sublease whose rentals are pledged by the issuer; and (b) The fixed rentals reserved under such lease or sublease will be sufficient to pay all of the expenses of the lessor in connection with the lease or sublease and the operation of the property and to pay principal and interest so as to retire the bonds during the fixed term of such lease or sublease or, if such fixed rentals are not sufficient, a governmental subdivision agrees to pay such required amounts;
(4) From revenue specifically pledged therefor of a public service operated by the borrowing entity if the entity is legally authorized and does obligate itself that rates of service will be fixed, maintained, and collected so as to produce revenue or earnings sufficient to pay all operating and maintenance charges and all principal and interest of such obligations in accordance with their terms; or
(5) From revenue specifically pledged therefor from excise taxes levied. Any investment authorized under this section shall have a minimum quality rating as described in subdivision (2) of section 44-5112.