When can Mrs. Pierce enroll in a Medicare Cost plan that offers Part D prescription drug coverage?

The enrollment in a Medicare Cost plan that offers Part D prescription drug coverage is governed by specific enrollment periods, which correlate with the broader Part D program guidelines. This means that Mrs. Pierce can only enroll during designated enrollment periods such as the Initial Enrollment Period, the Annual Enrollment Period, or Special Enrollment Periods, as specified for Part D.

These enrollment windows are established to help manage the flow of new enrollees and to ensure that beneficiaries have access to the necessary information to make informed decisions about their coverage. Therefore, the correct answer reflects the requirement to adhere to the enrollment periods set forth under the Part D program, ensuring that Mrs. Pierce can enroll in the plan and receive Part D coverage without facing penalties or interruptions in coverage.