; (ii) eligible for medical assistance under a State plan under title XIX; or (iii) enrolled for child health assistance or pregnancy-related assistance under a State plan under title XXI. (C) Regulations The Secretary shall promulgate a rule for determining residency for purposes of subparagraph (A). (3) Employer-sponsored plans (A) Employer enrollment Effective with respect to the first plan year that begins 1 year after the date of enactment of the Choose Medicare Act and each plan year thereafter, the Secretary shall provide options for Medicare part E plans in the small group market and large group market that are voluntary, and available to all employers. (B) Group health plans The Secretary, acting through the Administrator for the Centers for Medicare & Medicaid Services, at the request of a plan sponsor, shall serve as a third party administrator of a group health plan that is a Medicare part E plan offered by such sponsor. (C) Portability for employer-sponsored plans The Secretary shall develop a process for allowing individuals enrolled in a Medicare part E plan offered in the small group market or large group market to maintain health insurance coverage through a Medicare part E plan if the individual subsequently loses eligibility for enrollment in such a plan based on termination of the employment relationship. The ability to maintain such coverage shall exist regardless of whether the individual has the option to enroll in other health insurance coverage, including coverage offered in the individual market or through a subsequent employer. (d) Premiums The Secretary shall establish premium rates for the Medicare part E plans that— (1) are adjusted based on— (A) whether the plan is offered in the individual market, small group market, or large group market; and (B) the applicable rating area; (2) are at a level sufficient to fully finance— (A) the costs of health benefits provided by such plans; and (B) administrative costs related to operating the plans