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
100 women, followed up for 20 months, with OCPs, 5 became pregnant. Calculate the Pearl Index 
Select and explain. 
A. 1, B. 2, C. 3, D. 4
C: 3
Answer: C: 3 
Explanation: None