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?

The correct statements are sensors in the brain predict the lack of oxygen and the muscles in his body require more energy and thus more oxygen.  

Whenever one goes on a level very high from the Earth's surface like in mountains, the sensors in the brain finds out that there is less oxygen present at a higher level. Secondly, whenever a person performs some kind of strenuous activity like mountain trekking, the production of lactic acid takes place in the muscles. Thus, the body needs more oxygen at that time to fulfill the requirement, due to the two mentioned factors the person breathes heavier.  

c. glycolysis

explanation:

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