Living of frog
The adult frog has lungs, like other land vertebrates.
It is also able to absorb some oxygen through its skin.
Larval frogs (tadpoles) hatch in water from shell-less eggs laid in water, like those of fish, and develop gills, like fish, for the first stages of their life. Then they grow legs, grow lungs, their tail shrinks to nothing, their gills shrink to nothing, and they become adults.