endocrine and skeletal excretory and nervous circulatory and respiratory digestive and reproductive
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Which two body systems are involved in inhaling oxygen and exhaling carbon dioxide?
Possibilities:
- endocrine and skeletal
- excretory and nervous
- circulatory and respiratory
- digestive and reproductive

circulatory and respiratory