Q: Given a scientific passage and an answer, generate a question for the given answer.
Passage: The lungs release carbon dioxide into the air. Carbon dioxide is a gaseous waste product of the cells. Wastes are excreted from the body by the excretory system. Therefore, the lungs are organs of the excretory system as well as the respiratory system. Answer: both
A:
Are the lungs organs of the excretory system, the respiratory system, or both?