; (ii) the modernization, through energy efficiency improvements, of public housing units owned by the agency; or (iii) the construction, rehabilitation, purchase, or conversion of units to replace public housing units that are demolished or disposed of pursuant to section 18 or converted pursuant to section 22 or 33. (B) Terms Notes or other obligations guaranteed pursuant to this paragraph shall be in such form and denominations, have such maturities, and be subject to such conditions as may be prescribed by regulations issued by the Secretary. The term of such loan guarantee shall not exceed 20 years. (C) Limitation on percentage A guarantee made pursuant to this paragraph shall guarantee repayment of 95 percent of the unpaid principal and interest due on the notes or other obligations guaranteed. (D) Use of capital and operating funds Funds allocated to an issuer pursuant to this subsection or subsection (e) may be used for payment of principal and interest due (including such servicing, underwriting, or other costs as may be specified in regulations of the Secretary) on notes or other obligations guaranteed pursuant to this paragraph. (E) Repayment (i) Contract; pledge To ensure the repayment of notes or other obligations guaranteed under this paragraph and charges incurred under this paragraph and as a condition for receiving such guarantees, the Secretary shall require the issuer of any such note or obligation to— (I) enter into a contract, in a form acceptable to the Secretary, for repayment of notes or other obligations so guaranteed