A frog is an example of which type of animal?

A frog is classified as an amphibian, which is the accurate designation for this type of animal. Amphibians are characterized by their life cycles that typically include both aquatic and terrestrial stages. They usually begin their life as eggs laid in water, which hatch into larvae (such as tadpoles) that breathe through gills. As they mature, amphibians undergo metamorphosis, developing lungs for breathing air and often adapting to life on land.

The features of amphibians also include moist skin that allows for gas exchange and a dependence on water for reproduction. This distinguishes frogs from mammals, reptiles, and fish. While mammals and reptiles are predominantly land-dwelling and have different reproductive strategies, fish are fully aquatic and have characteristics such as scales and gills. The unique life cycle and physiological traits of frogs align them with the amphibian category, making D the correct answer.