b) He has damage to dorsal sensory neurons in the spinal cord.
Dorsal sensory neurons have processes that should perceive information about pain or touch. If they do not function, the patient cannot feel it. In addition, motor reflexes require perceiving of some stimulus. Problem with sensory neurons explains the inability to perceive stimuli.
Variant a) is incorrect because patient can move any part of the body.
Variant c) is incorrect because patient can make voluntary movements.
Variant d) is incorrect because patient can move any part of the body, which implies that motor neurons, which create output, function normally.