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
Percentage of para-para isomer in DDT is: 
Select and explain. 
A. 20-30%, B. 40-50%, C. 60-70%, D. 70-80%
B: 40-50%
Answer: B: 40-50% 
Explanation: 40-50%