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: Physiology
Normal prothrombin time is: 
Select and explain. 
A. 5-7 sec, B. 10-20 sec, C. 30 sec, D. 1 min
B: 10-20 sec
Answer: B: 10-20 sec 
Explanation: None