What is a primary characteristic of amphibians?

Amphibians are defined primarily by their unique life cycle, which typically includes both aquatic and terrestrial stages. This adaptability allows them to thrive in a variety of environments. For example, many amphibians start their life as eggs laid in water, where they hatch into larvae that live in aquatic habitats and eventually undergo metamorphosis to become adults capable of living on land. This dual capability is a fundamental characteristic of amphibians, distinguishing them from other animal groups. The other options do not accurately represent amphibians; they include traits associated with birds or marine-only species, which do not encompass the broader ecological niches that amphibians occupy.