This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bronchopulmonary Segments, Embryonic veins, Subject name: Anatomy
[{'content': 'what is the root value of phrenic nerve? \nSelect and explain. \nA. C3,4,5, B. C2,3,4, C. C4,5,6, D. C5,6,7', 'role': 'user'}, {'content': 'Answer: A \nExplanation: * Phrenic nerve (C3,C4,C5)- It descends in front of scalenus anterior muscle . * Descends down to enters thorax where it lies between subclan vein(in front) and subclan aery lies behind it . * Fuher it descends in front of hilum of the lungs (whereas vagus nerve descends behind the hilum of lungs) * It is mixed nerve sensory and motor.(both motor and sensory to diaphragm)', 'role': 'assistant'}]