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': 'Stage of labor lasting from full dilatation of cervix to complete bih of baby is? \nSelect and explain. \nA. 1st stage, B. 2nd stage, C. 3rd stage, D. 4th stage', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 2nd stage.', 'role': 'assistant'}]