It has to be nuclear fusion
Answer:
nervous system
While your heart is a vital organ, the brain (and the nervous system that attaches to the brain) make up the most critical organ system in the human body. The human nervous system is responsible for coordinating every movement and action your body makes.
You need to give some of the options that are given to you
Because it is easier to have a chain of command established with the staff if only one person is the leader. Companies and corporations also save money in the practice of only having a single leader or "boss."
I don't know if that answer will exactly help. :)