This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'The influence of maternal smoking and LBW incidence is studied. Detailed smoking history is taken at first AN visit and smoking history and bih weight were studied later. The type of study is- \nSelect and explain. \nA. Retrospective coho study, B. Cross sectinal study, C. Clinical trial, D. Prospective coho study', 'role': 'user'}, {'content': 'Answer: D \nExplanation: prospective coho studies is one which the outcome has not yet occurred at the time the investigation begins.most prospective studies begin in the present and continue into future. ref:park&;s textbook,ed 22,pg no 73', 'role': 'assistant'}]