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': 'Commonest cause of secondaryamenorrhea is : \nSelect and explain. \nA. TB, B. Pregnancy, C. Post pill amenorrhea, D. Anaemia', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Pregnancy', 'role': 'assistant'}]