The answer is B, the digestive system.
To solve this problem, all you need to do is define each system.
The circulatory system transports blood around the body.
The digestive system breaks down what you eat into waste or energy.
The nervous system sends messages to your brain when you want to do something.
The skeletal system protects your head with bones.
The answer would be the digestive system, because it breaks down your food into waste and energy.
Hope I helped! :)
