What defines an archipelago?

An archipelago is defined as a group of islands clustered together. This geographical feature typically consists of a collection of islands that may vary in size and are often located closely in a body of water, such as an ocean or sea. Archipelagos can be formed through various geological processes, including volcanic activity or the rising of sea levels, and they can host diverse ecosystems due to their varied landscapes and habitats.

In contrast, the other options describe different geographical or ecological concepts. A large mountainous region refers to a specific landform characterized by high elevation and rugged terrain, which does not relate to a collection of islands. An ecosystem found in wetlands implies a specific type of habitat characterized by water saturation, which does not pertain to the grouping of islands. A single island with multiple towns describes an individual landmass with human settlements, rather than a grouping of islands. Thus, the definition of an archipelago hinges on the concept of multiple islands in close proximity to one another.