(c)There is hereby established in the Treasury of the United States a sinking fund, the Kennedy Center Revenue Bond Sinking Fund (hereinafter referred to as the “Fund”), which shall be used to retire the obligations of the Board incurred under subsection (a) of this section upon the respective maturities of such obligations. The Board shall pay into the Fund, beginning onand ending on, the annual sum of $200,000 in amortization of the principal amount of the obligations. Such sums shall be invested by the Secretary of the Treasury in public debt securities with maturities suitable for the needs of the Fund and bearing interest at rates determined by the Secretary of the Treasury, taking into consideration the current average market yield on outstanding marketable obligations of the United States of comparable maturities. The interest on such investments shall be credited to and form a part of the Fund. Moneys in the Fund shall be used exclusively to retire the obligations of the Board incurred under subsection (a) of this section. Adjustments of not greater than plus or minus 5 per centum may be made from time to time in the annual payments to the Fund in order to correct any gains or deficiencies as a result of fluctuations in interest rates over the life of the investments: Provided, however, That a final adjustment shall be made between the Board and the Secretary of the Treasury at the end of the amortization period to correct any overall gain or deficiency in the Fund. The terms of this adjustment shall be covered by a memorandum of understanding between the Board and the Secretary of the Treasury to be consummated on or before the time the initial payment into the Fund is made.