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': 'Which events occurred before 1900AD -a) Establishment of seat of social medicine at Oxfordb) Epidemiological work on cholera by John Snowc) Work on scurvy by James Lindd) Use of BCG vaccinee) Chadwick work on cholera in London \nSelect and explain. \nA. ed, B. dca, C. bce, D. ac', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]