Final answer:
Frogs are amphibians that begin their life as tadpoles and undergo metamorphosis to become adult frogs.
Step-by-step explanation:
The amphibian that begins its life as a tadpole is the frog. Frogs are a type of amphibian that undergoes metamorphosis from a tadpole to an adult frog. Tadpoles have gills, a long tail, and no legs. As they undergo metamorphosis, they develop limbs, lose their tails, and develop lungs, preparing them for life on land as adult frogs.