Which specialized structures allow dolphins to breathe? A. Watertight eggs
O B. Gills
C. Lungs
D. Milk-producing glands

lungs

Explanation:

they don't have gills, and the milk producing glands and watertight eggs have nothing to do with it

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.