muscular and skeletal nervous and endocrine excretory and digestive circulatory and respiratory
I gave my students this multiple choice question: Which human body systems work together to send messages?

Only one answer is correct among these 4 choices:
- muscular and skeletal
- nervous and endocrine
- excretory and digestive
- circulatory and respiratory

Could you tell me which one is correct?

nervous and endocrine