The anterior root of a spinal nerve contains

The anterior root of a spinal nerve contains axons from the motor neurons.

Explanation:

A spinal nerve is a mixed nerve and consists of many nerve fibers from both the dorsal and the ventral or anterior roots.

The anterior or the ventral motor neurons are present in the grey matter of the spinal cord. The anterior root of a spinal nerve consists of the axons from motor neurons.

Thus, the anterior root of a spinal nerve consists of axons from the motor neurons.