The correct answer is: A. Digestive System
The mesoderm is the middle layer of cells that forms in the embryo. It gives rise to many different tissues and organs in the body, including the digestive system. The digestive system is responsible for breaking down food and absorbing nutrients. It is made up of the mouth, esophagus, stomach, small intestine, large intestine, and rectum.
The nervous system is responsible for controlling the body’s movements and for processing information from the senses. It is made up of the brain, spinal cord, and nerves.
The circulatory system is responsible for transporting blood throughout the body. It is made up of the heart, blood vessels, and blood.
The lining of the gut is a thin layer of cells that lines the inside of the digestive system. It helps to protect the digestive system from harmful substances and to absorb nutrients.
In coelenterates, the mesoderm gives rise to the digestive system. The digestive system is a simple tube that runs from the mouth to the anus. It is lined with cells that secrete digestive enzymes and absorb nutrients. The digestive system is responsible for breaking down food and absorbing nutrients.