Circulatory system
Excretory system
Reproductive system
Respiratory system
Answer is Wrong!
Answer is Right!
The correct answer is D. Respiratory system.
Alveoli are tiny air sacs in the lungs where gas exchange takes place. The lungs are part of the respiratory system, which is responsible for exchanging oxygen and carbon dioxide between the blood and the air.
The circulatory system is responsible for transporting blood throughout the body. The excretory system is responsible for removing waste products from the body. The reproductive system is responsible for reproduction.