The Medicare program has multiple parts covering different services.

Medicare Part B provides coverage for outpatient services, including physician services, preventive care, outpatient procedures, diagnostic tests, and durable medical equipment. Part B is a key component of Medicare, covering medically necessary services and some preventive services.

A. Part C (Medicare Advantage) includes all benefits and services covered under Parts A and B and often additional services, but it is provided through private insurance companies.

C. Part A covers inpatient hospital care, skilled nursing facility care, hospice, and some home health services.

D. Part D provides coverage for prescription drugs.

Therefore, the correct answer is B. Part B.