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
[{'content': 'Safe period in rhythms method is : (In a female with 28 days menstrual cycle) : \nSelect and explain. \nA. Initial 14 days, B. Later 14 days, C. First and last 7 days, D. 10 to 21 days of the cycle', 'role': 'user'}, {'content': 'Answer: C \nExplanation: First and last 7 days', 'role': 'assistant'}]