it was Louis Pasteur(1822-1895) a French chemist first discovered what causes illness hope this helps!
Answer:
Respiratory and circulatory
Explanation:
The Circulatory System Works in Tandem with the Respiratory System. The circulatory and respiratory systems work together to sustain the body with oxygen and to remove carbon dioxide. Pulmonary circulation facilitates the process of external respiration: Deoxygenated blood flows into the lungs.
Little food, limited oxygen in some areas, no sunlight, extreme cold temperatures
The answer would be D) fighting disease. Why D) u may ask? well its because number 1, A) making food doesn't really make animals healthy, some animals make their own supply of food and others just go find food rather than create so really no, number 2, B), getting enough sunlight doesn't make it healthy, some animals are underground or in the ocean, so they really don't need sunlight, some sea monsters below we don't know or seen yet have probably been down there without ever coming up for light so no, C) reproducing, animals reproducing wont really make them healthy at all, it will just make more of them so no. But D) yes because when their body fights against the disease it can help them stay healthy.
