This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'Which of the following will cause an increase in the prevalence of the disease - \nSelect and explain. \nA. Immigration of healthy persons, B. Increased cure rate of the disease, C. Longer duration of the disease, D. Emigration of diseased persons', 'role': 'user'}, {'content': 'Answer: C \nExplanation: P = I x D\nIncrease in incidence or duration of disease results in increased prevalence.', 'role': 'assistant'}]