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': 'As compared to a routine case-control study, nested case-control study avoids problems (in study design) related to - \nSelect and explain. \nA. Temporal association, B. Confounding bias, C. Need for long follow up, D. Randomization', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]