Answer: Feet and skin
Explanation:
The feet of the frog shows that it has gone through aquatic phase of life. The webbed feet of the frog shows that they need this kind of feet for swimming.
The feet of the frogs forms a web like structure that helps it to swim in water as well as move on the ground.
The semipermeable membrane of the frogs helps to keep the body hydrated as they do not drink water in spite of being in water partially.