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: Orthopaedics
[{'content': 'Ramu, an 8-year old boy presented with pain in the arm. On x-ray, his upper end of humerus demonstrates an expansile lesion in the metaphysis with breach of the overlying cortex. Most likely diagnosis is - \nSelect and explain. \nA. Aneurysmal bone cyst, B. Unicameral bone cyst, C. Chondroblastoma, D. Osteoclastoma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Here the diagnosis is aneurysmal bone cyst because the overlying cortex is breeched, which is not seen in unicameral bone cyst.', 'role': 'assistant'}]