integumentary and circulatory systems digestive and reproductive systems endocrine and respiratory systems digestive and immune systems
I gave my students this multiple choice question: Which two body systems interact to produce antibodies that require essential amino acids?

Only one answer is correct among these 4 choices:
- integumentary and circulatory systems
- digestive and reproductive systems
- endocrine and respiratory systems
- digestive and immune systems

Could you tell me which one is correct?

digestive and immune systems