The links the brain to the rest of the body.
a. heart
b. brain
c. spinal cord
d. nervous system

Spinal cord because it is connected to the brain through the magnum forum.

The correct answer for the blank is- Spinal cords.

Spinal cord ( present within vertebral column) is the part of central nervous system that acts like a nerve center and connects brain to the rest of body parts.

It carries sensory information to the brain in the form of nerve impulses and the motor information ( that is produced by brain) to the respective areas of the body.

By doing so, it links the brain to the rest parts of the body.

the answer is "a.) well–developed vascular system."

explanation:

answer( increase) their individual contractile activity;