Which geological feature is associated with subduction zones?

Subduction zones are regions where one tectonic plate is being forced underneath another, leading to distinct geological features. Ocean trenches are the most characteristic feature associated with these zones. As an oceanic plate subducts beneath a continental or another oceanic plate, it creates deep underwater trenches in the ocean floor. These trenches can be several kilometers deep and are some of the deepest parts of the Earth's surface.

The process of subduction is also responsible for several other geological phenomena such as volcanic activity, the formation of mountain ranges, and seismic activity, but the defining feature that directly illustrates the action of subduction is the presence of ocean trenches. Thus, ocean trenches are a clear indicator of where subduction occurs, making them the correct choice in this context.