circulatory, excretory, and respiratory circulatory, endocrine, and reproductive skeletal, muscular, and nervous skeletal, digestive, and respiratory
I gave my students this multiple choice question: Which human body systems work directly together to allow locomotion?

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

Could you tell me which one is correct?

skeletal, muscular, and nervous