Final answer:
The 'brick and mortar' pharmacy must be registered with the DEA, as it dispenses medications and controls the inventory, whereas the Internet site, which serves only for advertising and accepting orders, does not require DEA registration.
Step-by-step explanation:
In response to the question of which entities must be registered with the DEA in the scenario presented, the answer is a) The 'brick and mortar' pharmacy. According to the guidelines of the Drug Enforcement Administration (DEA), any facility that dispenses controlled substances must be registered with the DEA. In this case, even though the pharmacy operates an Internet site, it is the physical pharmacy that holds the inventory of drugs, including non-controlled prescription and over-the-counter (OTC) medications, and therefore must be registered.
It should be noted that the Internet site itself is not directly dispensing any drugs. Instead, it serves as advertising and a platform for receiving orders which are then fulfilled by the physical pharmacy. Consequently, the site itself does not require DEA registration; it is the dispensing brick and mortar pharmacy that bears this responsibility because it is the entity that ultimately handles the drugs.
Furthermore, pharmacists are healthcare professionals who are crucial in advising both physicians and patients about medication usage, interactions, and side effects. Their extensive knowledge in chemistry and biology is vital to providing this service, and that's why they must work in settings that comply with DEA regulations if they handle controlled substances.