This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics and Health, Subject name: Social & Preventive Medicine
[{'content': 'What is the study design used for Consanguineous marriage and genetic abnormalities? \nSelect and explain. \nA. Twin study, B. Family study, C. Case control study, D. Nested case control study', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Nested case control study: It is a small case control study nested in a big coho study Done for: 1. New and rare diseases 2. Diseases for which diagnostic tests are very expensive', 'role': 'assistant'}]