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': 'A screening test applied for colon cancer. Total population taken is 1000. Test is positive in 320 and test is negative in 680. 60 people actually had the disease among 320 and 20 had disease among the 680. Calculate positive predictive value. \nSelect and explain. \nA. 12%, B. 81%, C. 75%, D. 28%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]