This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Upper Extremity, Subject name: Anatomy
[{'content': "An 11-year-old boy falls down the stairs. A physician examines a radiograph of the boy's shoulder region. If the structure indicated by the letter B is fractured, which of the following structures is most likely injured? \nSelect and explain. \nA. Musculocutaneous nerve, B. Radial nerve, C. Deep brachial artery, D. Posterior humeral circumflex artery", 'role': 'user'}, {'content': 'Answer: D \nExplanation: (d) Fracture of the surgical neck of the humerus occurs commonly and damages the axillary nerve and the posterior humeral circumflex artery.', 'role': 'assistant'}]