Medicare Part B primarily covers which of the following types of treatment?

Medicare Part B is designed to provide coverage for a variety of outpatient services. It primarily covers outpatient hospital treatment, which encompasses a wide range of medical services such as physician visits, diagnostic tests, outpatient surgeries, preventive services, and certain therapies. This is essential for beneficiaries who may not need to be admitted to a hospital but still require medical attention or procedures that can be performed outside an inpatient setting.

In contrast, the focus of Medicare Part A is on inpatient hospital treatment, which includes coverage for hospital stays, skilled nursing facilities, and some home health care. Long-term care is generally not covered by Medicare in the sense of custodial care, which typically entails assistance with daily living activities. Lastly, while Medicare does have a Part D option for prescription drug coverage, pharmaceuticals are not covered under Part B apart from certain specific medications given in a doctor's office or outpatient hospital setting.

Thus, the correct answer reflects the primary function of Medicare Part B in handling outpatient services rather than inpatient or long-term care, and it clearly indicates the types of medical treatment readily accessible to beneficiaries under this part of the program.