Before marketing a new drug that has been approved for use based on clinical effectiveness and safety, the manufacturer wishes to study the potential new uses for the drug. This is an example of which phase of study?

a) Phase I studies focus on assessing the safety, dosing, and side effects of a drug in healthy volunteers, not its clinical effectiveness or potential new uses. b) Phase II studies evaluate the drug's effectiveness and safety in a small group of patients with the targeted condition but do not focus on potential new uses. c) Phase III studies are large-scale trials conducted to confirm the drug's effectiveness and safety before approval but do not typically involve studying new uses of the drug. d) Phase IV studies occur after a drug has been approved and marketed. These studies, often called post-marketing surveillance, evaluate the drug's effectiveness and safety in the general population and investigate new potential uses or long-term effects.