This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Non communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'Billings method is for - \nSelect and explain. \nA. Screening, B. Contraception, C. Aboion, D. None', 'role': 'user'}, {'content': "Answer: B \nExplanation: Cervical Mucus method Also known as 'Billing' s Method' or 'Ovulation method' Based on changes in characteristics of cervical mucosa 1.At ovulation : Watery, clear, smooth, slippery, profuse (like egg White) 2. After ovulation : Thickens and lessens in quantity Ref: Park 25th edition Pgno : 559", 'role': 'assistant'}]