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: Gynaecology & Obstetrics
[{'content': 'A child is diagnosed with osteosarcoma based on sunray appearance on X-ray. This is because of: \nSelect and explain. \nA. Calcification along the periosteum, B. Calcification along the blood vessels, C. Periosteal reaction, D. Soft tissue invasion', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. c. Periosteal reaction', 'role': 'assistant'}]