Answer:
The most important are the lungs, more precisely the alveoli.
Explanation:
Alveoli are structures of the lungs where gas exchange occurs. They allow oxygen from the air to pass into blood. Oxygen diffuses through the walls of alveoli into the capillaries that surround it. Oxygen is then bonded with the iron in red blood cells and travels to the heart. The heart then sends the oxygenated blood out to all the cells in the body.
<span>Controlled variable is a variable that was made constant in the research. That was because the controlled variables can influence the dependent or independent variable. If the variables is not made constant, it can alter the research result and made it invalid.
In this case, </span>the caffeine and alcohol intake might alter the physical activity or the blood glucose so it should be controlled.
Answer: D
Explanation: just did it on edg
