Double? Sorry I know nothing about this and just wanted to try to help
Answer:
The skull protects the brain from any direct damage and the vertebrae helps keep the nerves in the spine in place and protected from damage. So the central nervous system is protected by the vertebrae and the skull.
It can be a home gym because during free time he can do it so it can give him good results.
Answer:
U kept in the wrong gene,
And I am sorry I don't know the answer