Answer:
D. right radial nerve at the humerus
Explanation:
This man's symptoms indicate that he injured the muscles provided by the radial nerve. The radial nerve is the most important terminal branch of the brachial plexus, being responsible for the sensory innervation of the hand and motor of the arm and forearm.
A traumatic injury to the radial nerve is often caused by humeral fractures, as the nerve and bone are in close anatomical contact. Since, the 40-year-old man had weakness and numbness in his right hand, his examination revealed moderate weakness of the brachioradialis muscle and an inability to extend the wrist and fingers. We can conclude that the man has a right radial nerve injury in the humerus.