Final answer:
The brain and the spinal cord constitute the Central Nervous System (CNS), which is responsible for processing and coordinating bodily functions. The correct answer to the question is D. Central nervous system.
Step-by-step explanation:
The central nervous system.
The brain and the spinal cord make up the Central Nervous System (CNS). This is distinguished from the Peripheral Nervous System (PNS), which comprises a network of nerves extending throughout the body connecting the CNS to muscles, organs, and sensory systems. The CNS is the major structural and functional part of the nervous system that coordinates and controls the activities of the body. The PNS is further subdivided into the somatic nervous system, responsible for voluntary movements, and the autonomic nervous system, which regulates involuntary body functions. Therefore, in response to the question presented, the correct option is D. Central nervous system.