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: ENT
The muscle most responsible for the abduction of the vocal folds is the: 
Select and explain. 
A. Arytenoid, B. Cricothyroid, C. Lateral cricoarytenoid, D. Posterior cricoarytenoid
D: Posterior cricoarytenoid
Answer: D: Posterior cricoarytenoid 
Explanation: The posterior cricoarytenoid is the only muscle that abducts the the vocal folds. This muscle is innervated by the inferior laryngeal nerve, which is a continuation of the recurrent laryngeal nerve. If this muscle is denervated, the vocal folds may be paralyzed in an adducted position, which would prevent air from entering the trachea. Arytenoid, lateral cricoarytenoid, and thyroarytenoid all adduct the vocal folds. Cricothyroid is the only laryngeal muscle innervated by the external branch of the superior laryngeal. It tenses the vocal ligaments by tipping the thyroid cailage forward relative to the cricoid cailage.