Answer:
I think imma go with 1) Neurological development
Exposure to radiation and toxins. This is because the radiation can basically fry the sperm causing many reproductive issues in men.
Animals expel energy to keep warm
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.
