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': 'Case control study, All can be measured except - a) Relative risk b) Incidence c)  Odds ratiod)  Cause & effect relation \nSelect and explain. \nA. cb, B. b, C. abd, D. da', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]