Joel is studying a certain organ system of the human body. It interacts with the respiratory system to transport oxygen and carbon dioxide gases between the lungs and different parts of the body. It interacts with the digestive system to transport nutrients throughout the body, and it interacts with the urinary system to remove wastes from the body. What is Joel studying?

A. the nervous system
B. the circulatory system
C. the skeletal system
D. the muscular system