Answer:
A barter system is an old method of exchange. Th is system has been used for centuries and long before money was invented. People exchanged services and goods for other services and goods in return.
Explanation:
Answer:
The cardiovascular system helps maintain homeostasis by continually supplying the central nervous system--the brain and spinal cord--with oxygen and glucose. Brain cells start dying after just one minute without oxygen. The brain is the control center for all of the body's homeostatic processes.
A. genetic make-up and biochemistry