In healthcare, the following options can be considered customers:
- Option A: Doctors (they are customers when purchasing medical supplies, equipment, and services)
- Option B: Payers (insurance companies and other entities that pay for healthcare services)
- Option C: Pharmacy benefits managers (they manage drug benefits and are involved in negotiations, thus acting as customers)
- Option D: Patients (they are the end-users of healthcare services)
Option E (Ad agencies) typically do not fall under the category of customers in the traditional healthcare sense, as they are service providers rather than consumers of healthcare services.
So, the correct selections are A, B, C, and D.