; and (ii) by a geographic adjustment factor to address regional affordability concerns. (D) Authority to calculate amounts of monthly premiums separately for different ages In determining the annual premium amount under this paragraph for months in a year, the Secretary may make separate determinations of such amount for individuals by age, if the Secretary determines that making such separate determinations would increase enrollment under this section and reduce the risk of adverse selection. (3) Additional premium for certain part D plans Nothing in this section shall preclude an individual from choosing a prescription drug plan which requires the individual to pay an additional amount (because of the inclusion of supplemental prescription drug benefits or because the plan is a more expensive plan, pursuant to section 1860D–13(a)(1)). In such case, the monthly premium under paragraph (1) shall be increased with respect to such individual. (d) Payment of premiums (1) Payment Premiums for enrollment under this section shall be paid to the Secretary at such times, and in such manner, as the Secretary determines appropriate. (2) Deposit Amounts collected by the Secretary under this section shall be deposited in the Medicare Buy-In Trust Fund established under subsection (e). (e) Medicare Buy-In Trust Fund (1) In general There is hereby created on the books of the Treasury of the United States a trust fund to be known as the Medicare Buy-In Trust Fund (in this subsection referred to as the Trust Fund ). The Trust Fund shall consist of such gifts and bequests as may be made as provided in section 201(i)(1) and such amounts as may be deposited in, or appropriated to, such fund as provided in this title. (2) Premiums Premiums collected under subsection (d) shall be transferred to the Trust Fund. (3) Incorporation of Provisions Subsections (b) through (i) of section 1841 shall apply with respect to the Trust Fund and this title in the same manner as they apply with respect to the Federal Supplementary Medical Insurance