This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Natural Methods, Barrier Methods, IUDs, OCPs, Subject name: Social & Preventive Medicine
A woman has her shoest cycles of 26 days and longest cycle of 31 days. Calculate her unsafe period using Rhythm method ? 
Select and explain. 
A. 21-Aug, B. 20-Sep, C. 19-Aug, D. 22-Aug
A: 21-Aug
Answer: A: 21-Aug 
Explanation: Rhythm method: Aka calender method / safe period method / feile period method. Unsafe period = (Shoest cycle -18 days) to (longest cycle-10 days) Given shoest cycle = 26days; longest cycle = 31 days Unsafe period = to days = 8-21 days.