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': 'Hospital acquired infection of surgical wound is mostly by \nSelect and explain. \nA. Doctor, B. Instruments, C. Patient, D. Air borne', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]