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
Which muscle has the phrenic nerve on its anterior surface? 
Select and explain. 
A. Sternocleidomastoid, B. Anterior digastric, C. Superior belly of the omohyoid, D. Anterior scalene
D: Anterior scalene
Answer: D: Anterior scalene 
Explanation: The phrenic nerve lies on the anterior surface of the anterior scalene muscle. The nerve is held tightly against the surface of the muscle by the deep cervical fascia The roots of the brachial plexus and the subclavian artery pass posterior to the anterior scalene muscle and anterior to the middle scalene muscle.