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: Forensic Medicine
Symptoms of CO poisoning stas when the concentration is: 
Select and explain. 
A. < 10%, B. > 10%, C. > 20 %, D. > 40 %
B: > 10%
Answer: B: > 10% 
Explanation: Ans. > 10%