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
what is the root value of phrenic nerve? 
Select and explain. 
A. C3,4,5, B. C2,3,4, C. C4,5,6, D. C5,6,7
A: C3,4,5
Answer: A: C3,4,5 
Explanation: * 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)