Final answer:
Hospitals are the most likely to submit a Medicare Part A claim.
Step-by-step explanation:
Medicare Part A is a component of the Medicare program, which provides health insurance for individuals aged 65 and older. Medicare Part A primarily covers hospital charges for eligible individuals. Therefore, the most likely entity to submit a Medicare Part A claim would be hospitals. Doctors, pharmacies, and patients are not the ones who typically submit Medicare Part A claims.