Final answer:
Dorsal roots exclusively carry sensory fibers, while ventral roots exclusively carry motor fibers. Therefore, the correct answer is B) Motor / Sensory.
Step-by-step explanation:
The fibers in the dorsal and ventral roots have distinct functions. The dorsal roots contain the axons of sensory neurons that carry sensory information from the periphery of the body to the spinal cord. These are referred to as afferent pathways. In contrast, the ventral roots consist of axons from motor neurons that emerge from the anterior horn of the spinal cord, and their function is to send action potentials to skeletal muscles, which is an efferent pathway.
Therefore, the correct answer to the question is:
A) Dorsal roots - Sensory fibers
B) Ventral roots - Motor fibers
Spinal nerves are a mix of these fibers, but when they approach the spinal cord, they separate into these two types of roots, each strictly conveying either sensory or motor information. The radial nerve, as an example, contains both types of these fibers, illustrating how after the spinal nerves emerge, they can carry mixed signals to their target regions.