Jon likes hiking. He observes that whenever he hikes up a hill, he breathes heavier than when he is on flat ground. Which two statements explain why this happens?

A.) Sensors in the brain detect a lack of oxygen.

B.) The muscles in his body need more energy and therefore more oxygen.

C.) The body has too little carbon dioxide to maintain function.


D.) The body is using carbon dioxide instead of oxygen to make energy.

E.) Blood pressure has decreased, so less blood is being pumped to the muscles.