What defines fjords?

Fjords are characterized primarily by their deep inlets, which are formed by glacial activity. The distinctive feature of fjords is their steep cliffs or slopes that rise dramatically from the water. This geological formation occurs when glaciers carve out deep valleys as they move, and when they retreat, these valleys get filled with seawater, creating the scenic inlets known as fjords.

The other options describe different geographic features. Shallow coasts with sandy beaches, for instance, refer to coastal areas that have gentle slopes and are easily accessible, contrasting with the steep sides of fjords. Open seas popular with sailors are broader marine areas without the confined, enclosed nature of a fjord. Wide river valleys, meanwhile, are typically flat areas formed by river erosion, which are distinct from the dramatic and steep topography associated with fjords. This is why the correct answer highlights the unique characteristics of fjords that distinguish them from other geographic formations.