The second line of defense of the immune system, also an aspect of innate immunity, is the nonspecific resistance. These defense mechanisms destroy invaders in a general way and do not target specific antigens.
C) Joining a club, as that is a social organization.
The answer is tighten and contract.
In order for the students to pull the rope their muscles will need to tighten and contract so they are able to continuously pull with all their strength and power. Relaxed or twitched muscles will result in release of the rope.
