muscular and nervous excretory and respiratory circulatory and endocrine digestive and reproductive
I gave my students this multiple choice question: Which human body systems are most directly involved when a person is walking?

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

Could you tell me which one is correct?

muscular and nervous