Final answer:
The subarachnoid space contains D. cerebrospinal fluid (CSF).
Step-by-step explanation:
The subarachnoid space, which is found between the arachnoid and pia maters, contains cerebrospinal fluid (CSF). CSF is a clear bodily fluid that surrounds and cushions the brain and spinal cord. It also plays a role in removing metabolic waste from nervous tissue and circulating chemical substances throughout the brain and spinal cord.
White matter refers to the axons in the CNS that are covered in myelin sheaths, while gray matter refers to the regions of the CNS that primarily contain cell bodies and interneurons. While both white and gray matter are present in the CNS, they are not found within the subarachnoid space. Neurons, on the other hand, are the functional units of the nervous system and are present throughout the CNS in both white and gray matter. Therefore the correct answer is D. cerebrospinal fluid (CSF).