B.
Viruses are classified as biological agents instead of a living things, $& they are only made of genetic material.
Answer:
<em>Metabolism</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em><em>.</em>
Answer: Well really the digestive, respiratory and circulatory systems all work together to make cellular respiration possible so i guess you could choose a or b
Explanation:
I just looked it up, it's carbon!
