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': 'Meningococcal vaccine - \nSelect and explain. \nA. ACW135Y, B. ABCW135, C. CYW135 B, D. ABCY', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]