This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
[{'content': 'Random error- \nSelect and explain. \nA. Systemic error, B. Bias, C. Confounding factor, D. Reduces precision', 'role': 'user'}, {'content': 'Answer: D \nExplanation: .', 'role': 'assistant'}]