Chordates are any organisms that have a:

A) brain.
B) spinal cord.
C) peripheral nervous system.
D) brain and a spinal cord.

Chordates

A large phylum of animals that includes all vertebrates and some invertebrates, characterized by having a notochord at some stage in their development.

Spinal Cord

A long, thin, tubular structure made up of nervous tissue, which extends from the brainstem down the back, and is encased in the vertebral column, transmitting nerve signals between the brain and the rest of the body.

Brain

The organ located in the head of an animal that coordinates its behavior, processes sensory information, and is the center of perception, memory, thought, and emotion.