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': 'The following is true of brachial plexus: \nSelect and explain. \nA. Cervical rib involves lateral cord, B. Musculocutaneous nerve arises from medial cord, C. Radial nerve arises from posterior cord, D. Post fixed plexus is formed by C45678 and T1', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C - B.D. Chourasia, Vol.l, 4th ed, p. 51,52', 'role': 'assistant'}]