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': 'During pregnancy there is an increased respiratory sensitivity to Carbon dioxide due to higher circulating levels of : \nSelect and explain. \nA. Progesterone, B. Estrogen, C. Estriol, D. Prolactin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Progesterone', 'role': 'assistant'}]