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
Pearl index is 
Select and explain. 
A. Failure rate / 1 women years, B. Failure rate/10 women years, C. Failure rate/100 women years, D. Failure rate/1000 women years
C: Failure rate/100 women years
Answer: C: Failure rate/100 women years 
Explanation: Failure rate/100 women years