Stella’s respiratory system is not working well. Why is this a problem for her ability to exercise? A) Her respiratory system will not be able to break down molecules from air into oxygen.
B) Her cells will not work well when they have low levels of oxygen.
C) Her digestive system will have to work twice as hard to get the same amount of energy from glucose molecules.
D) Her cells will not work because molecules from air will be too large for her body to use.

In addition to giving an answer, please provide an explanation to support it.

I think the answer is A

Explanation:

since you have not provided the options here i   am going to give you general overview about hormone.hormone are actually the part of endocrine system in our body and produced by the endocrine glands. the hormones act like a chemical messenger   within human body. once produce by the glands they   travel through the blood stream and reach at specific or target tissue and organs   which result in control of our body function. the hormones are specific in their work and work on only the targeted tissue or organ   . with the of hormone endocrine system regulate the heart rate , metabolism, our mood and   growth as well as the development and even the sleeping cycle etc. they actually are the messenger for body cell and organs .