This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Integrated QBank, Subject name: Anatomy
A 40-year-old male patient presented to the ER with pain and deformity in the left arm after having a fall 2 hours ago. The doctor ordered an x-ray of the affected area. The nerve most likely involved in the above condition supplies which of the following marked muscles: - 
Select and explain. 
A. Muscle B, B. Muscle A, C. Muscle D, D. Muscle C
B: Muscle A
Answer: B: Muscle A 
Explanation: This is a case of fracture of surgical neck of humerus. The nerve involved is axillary nerve. Muscle supplied by axillary nerve are teres minor and deltoid.