What is a trench?

• A. A shallow depression on the continental shelf.
• B. A deep, narrow depression in the ocean floor formed at a subduction zone.
• C. A plateau of raised seabed.
• D. A volcanic island chain.

Answer: (B)

A trench is a deep, narrow valley on the ocean floor that forms where one tectonic plate dives beneath another at a subduction zone. The sinking of the oceanic plate into the mantle pulls the surface down, creating one of the deepest and most elongated features on Earth. These trenches mark the edges of convergent plate boundaries and are often located near volcanic arcs and intense seismic activity.

This description matches what trenches are: they’re not shallow shelves or raised plates, nor are they chains of volcanic islands. A shallow depression on the continental shelf is a much different, shallower feature, a plateau of raised seabed is not a trench, and a volcanic island chain forms from volcanic processes at hotspots or along different plate interactions.