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: Anatomy
[{'content': 'Which embryonic structure forms first? \nSelect and explain. \nA. Philtrum of upper lip., B. Frontonasal process, C. Maxillary process, D. Mandibular process', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]