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: Surgery
[{'content': "Guerin's sign is: \nSelect and explain. \nA. Ecchymosis at greater palatine foramen, B. Ecchymosis at mastoid foramen, C. Ecchymosis at condylar region, D. Ecchymosis at infraorbital foramen", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]