Arunner is three quarters of the way through a marathon. which systems are working to maintain oxygen levels for the runner's muscles?
a. integumentary, excretory, nervous, endocrine
b. circulatory, excretory, nervous, endocrine
c. respiratory, excretory, nervous, endocrine
d. circulatory, respiratory, nervous, endocrine

option D : circulatory, respiratory, nervous, endocrine

Explanation:

The circulatory system of the body maintains the flow of oxygen, nutrients and blood in the body. The respiratory system allows the uptake of oxygen and exhalation of carbon dioxide. Thus maintaining oxygen requirement of the runner. The nervous system regulates the process of breathing in the body. The endocrine system provides signals that works together with respiratory system.

The integumentary system comprises nail, skin, exocrine glands and hairs. The excretory system involves removal of waste from the body. Thus, option D is correct.

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