The answer is a. Nitrogen
<span>Macrophages work slowly apexBacteria reproduce quickly.</span>
Simple....
as you've learned... cells create tissue..tissue creates organs...organs create organ systems..and organ systems create organisms. They all work together to create something...
An example:
muscle cell-->>muscle tissue-->>heart-->>circulatory system-->>the circulatory system makes up a part of the body.
Thus, your answer.
