circulatory system excretory system immune system nervous system
I gave my students this multiple choice question: The digestive system breaks food down into molecules that are used by our body's cells. Which other body system regulates how fast or slow the digestive system functions?

Only one answer is correct among these 4 choices:
- circulatory system
- excretory system
- immune system
- nervous system

Could you tell me which one is correct?

nervous system