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: Anatomy
Muscle which helps in opening of the mouth: 
Select and explain. 
A. Lateral pterygoid, B. Medial pterygoid, C. Temporalis, D. Masseter
A: Lateral pterygoid
Answer: A: Lateral pterygoid 
Explanation: Lateral PterygoidThe primary function of the lateral pterygoid muscle is to pull the head of the condyle out of the mandibular fossa along the aicular eminence to protrude the mandible.A conceed effo of the lateral pterygoid muscles acts in helping lower the mandible and open the jaw whereas unilateral action of a lateral pterygoid produces contralateral excursion, usually performed in conce with the medial pterygoidsUnlike the other three muscles of mastication, the lateral pterygoid is the only muscle of mastication that assists in depressing the mandible (opening the jaw).At the beginning of this action it is assisted by the digastric,mylohyoid and geniohvoid muscles.