; and (ii) the level of benefits paid may be adjusted periodically in order to reflect the mortality experience and the investment experience of the Fund, but only after the Fund has obtained a certification from a member of the American Academy of Actuaries that the adjustment is sustainable for the remaining lifetime of participants then receiving benefits, based on the mortality tables and interest rates prescribed under subparagraph (C) by the Secretary for that time. (C) Mortality tables and interest rates used requirements The regulations promulgated under subparagraph (A) shall include the following: (i) Mortality Tables (I) In general The Secretary shall prescribe mortality tables to be used in determining annuity payments made directly by the Fund. Such tables shall be based on the actual experience of insurance companies that issue group annuities and projected trends in such experience. In prescribing such tables, the Secretary shall take into account results of available independent studies of the mortality of individuals receiving annuities under group annuity contracts. (II) Periodic revisions of mortality tables The Secretary shall make revisions, to become effective as soon as practicable, in any mortality table in effect to reflect more recent actual experience of insurance companies that issue group annuities and projected trends in such experience. In revising such tables, the Secretary shall take into account the results of more recent available independent studies of the mortality and projected trends of individuals receiving annuities under group annuity contracts. (ii) Interest Rates The Secretary shall prescribe interest rates to be used in determining annuity payments made directly by the Fund. Such rates shall be based on the yields on investment grade corporate bonds with varying maturities and that are in the top 3 quality levels available. Interest rates shall be prescribed quarterly or more frequently, as determined by the Secretary. (5) Duty to address best practices The Commission