This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'Prolactin levels: \nSelect and explain. \nA. Lowest in pregnancy, B. Highest during pregnancy, C. Unaffected by pregnancy and lactation, D. Variable in every pregnancy', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Prolactin increases tremendously in pregnancy and this ensures lactation.', 'role': 'assistant'}]