Concept:The mammalian lungs are adapted for efficient gas exchange, but they do not expand on their own; they are elastic and move passively with the chest wall.
Explanation:The lungs contain numerous alveoli, providing a large surface area for gas exchange.
The internal surface is moist, which helps gases dissolve and diffuse easily.
The lungs are highly vascularized, with dense capillary networks that allow efficient oxygen and carbon dioxide exchange.
However, the lungs themselves are not actively expandable.
They expand passively when the diaphragm contracts and the intercostal muscles lift the rib cage.
Thus, "expandable lungs" is not a true characteristic of the lungs themselves.
Answer:B. expandable lungs