Nervous tissue without myelin is referred to as which of the following?

The correct choice is grey matter. In the central nervous system, grey matter primarily consists of neuronal cell bodies, dendrites, and unmyelinated axons. It is where synapses occur and is responsible for processing information. The lack of myelin in grey matter distinguishes it from white matter, which contains myelinated axons and is involved in the transmission of signals over long distances within the nervous system.

As for the other options, pia mater and dura mater refer to the protective coverings (meninges) of the brain and spinal cord, and they do not specifically describe types of nervous tissue. White matter, in contrast to grey matter, is characterized by the presence of myelinated axons, which facilitate the rapid transmission of electrical signals in the CNS.