Answer:
"Helps fight off infection" protein doesn't do that. Your white blood cells is what fights that for you.
You just carried out flex ion of the legs
The joint is the ball and socket hip joint
The heart functions as a <span>muscle that helps to pump oxygen around the body.
Hope this helps. (ノ◕ヮ◕)ノ*:・゚✧ </span>
The answer to your question is C.Viral