Answer: The fourth one, a person who has insulin.
Explanation:
El doctor receta las pastillas para tomar por las mañanas, antes de desayunar means 'the doctor prescribes the pills to take in the morning, before breakfast.' This would eliminate the person with the cast, because, well, you don't need pills for a cast. This would also eliminate a person with a cut, because unless it was infected, you wouldn't need pills. A person who is fasting wouldn't need pills because fasting is not eating, and you don't really need pills for that. But insulin is a type of disease, and that would make the most sense.
