Select the correct answer.
Kelvin's cow is showing signs of poor health. The cow is staying away from the herd and is not alert in its environment. The veterinarian believes
that the cow is affected by some type of infection. He also states that the lack of white blood cells in the cow is making it less resistant to the
infection. Which system of Kelvin's cow is not functioning properly?
A. muscular system
B. endocrine system
C nervous system
D. circulatory system