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': 'Double blind study means(1994) \nSelect and explain. \nA. Observer is blind about the study, B. Person or group being observed is blind about the study, C. Both observer and observed group is blind, D. Interpreters and analysers are blind about the study', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans: cRef: Park, 17th ed, p. 73 & 18th ed, p. 77', 'role': 'assistant'}]