Name three components of the human circulatory system.

• A. Lungs, liver, kidneys
• B. Brain, spinal cord, nerves
• C. Muscles, bones, cartilage
• D. Heart, blood vessels, and blood.

Answer: (D)

The circulatory system is made up of three main parts that work together to move blood through the body: the heart, blood vessels, and blood. The heart acts as a pump that pushes blood into the vessels. Blood vessels form a vast network—arteries, veins, and capillaries—through which blood travels to reach every tissue. Blood is the transport fluid that carries oxygen and nutrients to cells and removes wastes. The other options describe components of different organ systems (respiratory, nervous, or musculoskeletal) rather than the circulatory system as a whole, so the trio of heart, blood vessels, and blood best fits what the circulatory system includes.