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: Unknown
[{'content': 'Which nerve is a branch of a root of the brachial plexus? \nSelect and explain. \nA. Suprascapular nerve, B. Dorsal scapular nerve, C. Upper subscapular nerve, D. Lateral pectoral nerve', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The roots of the brachial plexus are the anterior rami of spinal nerves Cs-T1. These five roots form the three trunks of the plexus. Each trunk divides into an anterior and a posterior division. The divisions form the three cords of the brachial plexus. The dorsal scapular nerve is a branch of the C, root. The supra scapular nerve is a branch of the upper trunk. The upper subscapular nerve and the thoracodorsal (middle subscapular) nerve are branches of the posterior cord. The lateral pectoral nerve is a branch of the lateral cord.', 'role': 'assistant'}]