Median nerve injury at the wrist is commonly tested by-
Abductor pollicis brevis and flexor pollicis brevis, both are supplied by the median nerve. However, flexor pollicis brevis cannot be tested separately because flexion of metacarpophalangeal joint of the thumb (the function of flexor pollicis brevis) can also be produced by flexor pollicis longus. On the other hand abductor pollicis brevis can be tested separately.
Option 'c & d' are incorrect in regards to this question. Though, sensory loss over palm (lateral 2/3) and ring finger (lateral half) occurs in median nerve injtuy, these area are not used to test sensory loss. For testing, the sensory deficit in median nerve injury tip of the index and middle finger (autonomous zone) are used.
Contraction of abductor pollicis brevis
Contraction flexor pollicis brevis
Loss of sensation on palm
Loss of sensation on ring finger