**Core Concept**
The median nerve is a mixed nerve that supplies the anterior compartment of the forearm, including the thenar muscles, and the palmar surface of the hand. Its main function is to provide motor innervation to the muscles of the forearm and hand, as well as sensory innervation to the palmar surface of the thumb, index, middle finger, and part of the ring finger.

**Why the Correct Answer is Right**
The median nerve supplies the muscles of the thenar eminence (opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis), which are responsible for thumb movement. However, at the wrist level, the median nerve also supplies the lumbricals and the flexor digitorum profundus (for the index and middle fingers), but not the flexor digitorum superficialis (which is supplied by the median nerve in the forearm). The muscles that would be paralyzed in a median nerve injury at the wrist level are the thenar muscles and the lumbricals to the index and middle fingers.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a muscle that is not supplied by the median nerve at the wrist level. The flexor digitorum profundus for the index and middle fingers is actually supplied by the median nerve in the forearm.
**Option B:** This option is incorrect because it is a muscle that is not supplied by the median nerve at the wrist level. The flexor digitorum superficialis is supplied by the median nerve in the forearm, not at the wrist.
**Option C:** This option is incorrect because it is a muscle that is not supplied by the median nerve at the wrist level. However, this option is also not the best distractor because it is indeed a muscle that could be affected by a median nerve injury, but not the best choice given the options.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the median nerve supplies the thenar muscles and the lumbricals to the index and middle fingers, which are responsible for thumb movement and finger flexion.

**Correct Answer:** D.