Which type of plate boundary is most closely associated with deep ocean trenches?

Deep ocean trenches are primarily associated with subduction zones, which occur at convergent plate boundaries. In a subduction zone, one tectonic plate moves under another and sinks into the mantle. This process creates deep ocean trenches, which are some of the deepest parts of the Earth's oceans. The intense geological activity at these boundaries is a result of the oceanic plate, being denser than the continental plate, subducting beneath it.

Unlike divergent boundaries, where plates move apart and new oceanic crust is formed, or transform boundaries, which involve sliding past each other without significant vertical movement, subduction zones lead to the creation of trenches due to the downward movement of the subducting plate. Therefore, subduction is the correct association with deep ocean trenches.