The correct option is B Nervous
The brain serves as the center of the nervous system in all vertebrates and most invertebrate animals. Only a few invertebrates, such as sponges, jellyfish, adult sea squirts and starfish do not have a brain.In such organisms, a diffuse neural tissue is present. It is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste and smell. The brain is the most complex organ in a vertebrate's body.