This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concept of health and disease, Subject name: Social & Preventive Medicine
[{'content': '"Lead time" refers to the time between \nSelect and explain. \nA. Disease onset and final critical diagnosis, B. Disease onset and final possible point of detection, C. First possible point of detection and final critical diagnosis, D. First possible point of detection and usual time of diagnosis', 'role': 'user'}, {'content': "Answer: D \nExplanation: LEAD TIME is the advantage gained by screening, i.e., the period between diagnosis by early detection and diagnosis by other means. It is an impoant factor when evaluating the effectiveness of a specific test. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 148", 'role': 'assistant'}]