Answer:
4
Step-by-step explanation:
The circulatory system includes the blood that has picked up the carbon dioxide from all of the respiring tissues and who also delivered oxygen to them to continue respiring.
The blood will then reach the lung where the carbon dioxide that the tissues released is exchanged for oxygen in the alveoli.
* Blood cells isn't an organ system which makes 1 incorrect.
* Digestive system will in no way bring the blood to the lungs or away from it. This is the circulatory system's job. So 2 is incorrect.
*Lastly, lungs are organs and the question asks for organ systems. So 3 is incorrect.