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
The influence of maternal smoking and LBW incidence is studied. Detailed smoking history is taken at first antenatal visit and smoking history and bih weight were studied later. The type of study is - 
Select and explain. 
A. Retrospective coha study, B. Cross sectional study, C. Clinical trial, D. Prospective coho study
D: Prospective coho study
Answer: D: Prospective coho study 
Explanation: Ans. is 'd' i.e. Prospective coho study