4 is true with question you asked
They developed to be protected by the hard shell from parasites and ther predators.
The central nervous system (CNS), which is made up of the brain and the spinal cord, and the peripheral nervous system (PNS), which is comprised of nerves and ganglia (small concentrations of grey matter).
The brain sends messages to the peripheral nerves in the body via the spinal cord, these have control of muscles and internal organs.
This is because of B. Their cells are in direct contact with the environment.
