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: Dental
[{'content': 'The purpose of double blinding in clinical trials is to: \nSelect and explain. \nA. Achieve comparability between study and control groups, B. Avoid observer bias, C. Avoid subject bias, D. Avoid observer and subject bias', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Single blind:\xa0Only patients or only investigators are ignorant of assigned treatment.\nDouble blind: Patients & investigators are ignorant of assigned treatment.\nTriple blind: Patients, investigators & data evaluators are ignorant of assigned treatment.', 'role': 'assistant'}]