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
Which of the following natural family planning method is most effective? 
Select and explain. 
A. Basal body temperature, B. Cervical mucus method, C. Bilings method, D. Symptothermic method
D: Symptothermic method
Answer: D: Symptothermic method 
Explanation: Symptothermic method This method combines the temperature, cervical mucus and calendar techniques for identifying the feile period. If the woman cannot clearly interpret one sign, she can "double check" her interpretation with another. Therefore, this method is more effective than the "Billings method or cervical mucus method "