This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Surgery
In doing phrenic nerve block, it is best to infiltrate 
Select and explain. 
A. Scalenus anterior, B. Scalenus posterior, C. Posterior border of sternomastoid, D. Anterior border of sternomastoid
C: Posterior border of sternomastoid
Answer: C: Posterior border of sternomastoid 
Explanation: Phrenic nerve is blocked 3 cm above the clavicle at the posterior border of sternomastoid.