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': 'pH of the vagina is lowest during : \nSelect and explain. \nA. Ovulation, B. Menstruation, C. Pregnancy, D. Puerperium', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pregnancy', 'role': 'assistant'}]