This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Randomization means \nSelect and explain. \nA. Mixing of cases and controls, B. Selecting cases, C. Selecting controls, D. Vaccine and Erythromycin', 'role': 'user'}, {'content': "Answer: A \nExplanation: Randomization is a statistical procedure by which the study paicipants are allocated into groups usually called study and control groups; to receive or not receive an experimental preventive or therapeutic procedure, maneuver or intervention Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 90", 'role': 'assistant'}]