The human brain has up to 100 billion neurons (nerve cells)
The circulatory system is system in the human body that provides a network through which our blood flows constantly.The human cardiovascular system is considered closed because there are no holes for blood to enter or leave the system. Correct answer: D
In the closed circulatory system the blood stays confined within the vessels and heart.
D. All of the above. Because every being is totally different, meaning it will depend on your genetics from your family. :) <span />
