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': 'How many guinea worm cases were identified in the year 1999 - \nSelect and explain. \nA. 0, B. 9, C. 2000, D. 4000', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]