The lungs are major organs of which organ systems? the respiratory and endocrine systems the digestive and cardiovascular systems the excretory and respiratory systems the cardiovascular and immune systems

The lungs are a part of the respiratory system

The lungs are important for two reasons; they are responsible for respiration or breathing if you prefer, and they are also responsible for being the primary organ of maintaining the pH balance of the blood via breathing out CO2.

Under most circumstance I'd say the lungs are part of the circulatory and respiratory system. However you can actually consider them an integral part of Excretory as well.