The correct answer is: dorsal root

The dorsal root of a spinal nerve contains afferent sensory fibers, while the ventral root of a spinal nerve contains efferent motor fibers. The dorsal primary ramus, which is the first dorsal nerve branching from the spinal nerve, contributes motor innervation to the muscles of the back and gives off posterior cutaneous nerves which innervate the skin of the back. Although these cutaneous sensory nerves contain afferent fibers, there are no posterior cutaneous nerves on the skin of the hand, so this is not the correct answer. Finally, a gray ramus communicans is a structure that postganglionic sympathetic fibers use to leave the sympathetic chain ganglion to reach a ventral primary ramus.