Which country is both an island and a continent?

Australia is classified as both an island and a continent, making it unique in this regard. A continent is typically considered a large landmass, whereas an island is a smaller landform completely surrounded by water. Australia fits the criteria for both; it is the smallest continent and also the largest island in the world.

The distinction lies in the geological and geographical classification. While Australia is significant enough in size to be termed a continent, it is also surrounded by water, making it fulfill the criteria for being an island. It encompasses diverse ecosystems, landscapes, and climates, further emphasizing its vastness compared to the other options listed, which do not meet both criteria simultaneously.

In contrast, Japan, Greenland, and New Zealand are all categorized as islands but do not hold the status of continents. Greenland, while notably large, is considered a part of the North American continent rather than a standalone continent itself. Japan and New Zealand are also regarded purely as islands without the designation of a continental landmass. Thus, Australia stands out as the only choice that embodies both characteristics.