The body's nervous system is made up of the brain, the spinal cord, the retina, and many other nerves. The circulatory system is made up of the heart, arteries, veins, and capillaries. The nervous system tells the heart when to beat, and the circulatory system supplies nerve cells with blood.

Which of the following best describes the relationship between the nervous system and the circulatory system?
A.
The nervous system and the circulatory system do not affect each other.
B.
The nervous system is a subsystem of the circulatory system.
C.
The circulatory system is a subsystem of the nervous system.
D.
The circulatory system and the nervous system depend on each other.