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': 'Cervical ripening is mainly due to the action of : \nSelect and explain. \nA. PGE2, B. PGF2, C. PGI2, D. PGG7', 'role': 'user'}, {'content': 'Answer: A \nExplanation: PGE2', 'role': 'assistant'}]