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: Gynaecology & Obstetrics
Which natural family planning method is based on ogino knauss theory: 
Select and explain. 
A. BBT method, B. Rhythm method, C. Lactational anerorrhea, D. Withdrawl method
B: Rhythm method
Answer: B: Rhythm method 
Explanation: None