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': 'When launching a study, many respondents are invited, some of whom fail to come, this is called \nSelect and explain. \nA. Response bias, B. Volunteer bias, C. Selection bias, D. Berkesonian bias', 'role': 'user'}, {'content': 'Answer: A \nExplanation: .', 'role': 'assistant'}]