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
Median nerve injury at wrist, is commonly tested by- 
Select and explain. 
A. Contraction of abductor pollicis brevis, B. Contraction flexor pollicis brevis, C. Loss of sensation on palm, D. Loss of sensation on ring finger
A: Contraction of abductor pollicis brevis
Answer: A: Contraction of abductor pollicis brevis 
Explanation: Though the lateral three fingers, lateral half of ring finger and corresponding region of palm are supplied by median nerve, test for sensory loss by median nerve injury is done on the autonomous zone (Tip of middle and index fingers).
Flexion of thumb can also be produced by flexor pollicis longus. So for testing median nerve injury, abductor pollicis brevis is tested.