Question

A system is a group of related parts with specific roles that work together to achieve an observed result. Which of the following are the main parts of the circulatory system?

A.
red blood cells and white blood cells
B.
the human body and its organ systems
C.
the brain and spinal cord
D.
heart, blood, and blood vessels

Answer 1

D.

heart,blood,and blood vessels

Answer 2

D. heart , blood ,and blood vessels