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 of the following muscle produces abduction of vocal cord? 
Select and explain. 
A. Posterior cricoarytenoid, B. Lateral cricoarytenoid, C. Cricothyroid, D. Oblique arytenoids
A: Posterior cricoarytenoid
Answer: A: Posterior cricoarytenoid 
Explanation: Intrinsic muscles of larynx
 
Exceptions: 1. All are paired except transverse arytenoid
                       2. All lie internally except cricothyroid
A) Muscles which modify rima glottidis