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: ENT
[{'content': 'Mastoid infection which erodes through the outer cortex of bone results in - \nSelect and explain. \nA. Sub-periosteal abscess, B. Epidural abscess, C. Perichondritis, D. Lateral sinus thrombosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]