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': 'The most definite clinical sign indicating odontogenic infection in to the masticatory space is: \nSelect and explain. \nA. Trismus, B. Xerostomia, C. Difficulty in swallowing, D. Swelling in submental area', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]