The correct answer is a) epineurium, perineurium.
In the structure of nerves, fascicles, which are bundles of nerve fibers, are surrounded by a layer called the perineurium. This layer provides a protective barrier and maintains the biochemical environment necessary for nerve conduction. The entire nerve, which is made up of multiple fascicles, is covered by a tougher, more protective layer known as the epineurium. This outer layer contains blood vessels and serves to protect the entire nerve from physical damage. Understanding these layers is important for comprehending how nerves are structured and how they function within the body.