Final answer:
Deep-sea trenches are found near volcanic arcs because they are commonly situated at convergent plate boundaries where subduction occurs, resulting in volcanism close to coastlines.
Step-by-step explanation:
Deep-sea trenches are geologic formations on the ocean floor commonly found at convergent plate boundaries where one plate is being pushed below another in a process known as subduction. As a plate subducts, it is forced into the upper mantle and produces a topographic depression in the sea floor, which forms the trench. Given the association of subduction zones with trenches and volcanic activity, volcanoes in such zones are closer to coastlines because the partial melting of the asthenosphere above the subducting slab leads to volcanism and hence formation of a volcanic arc parallel to the trench and near the edge of the continent or island arc it abuts.
Therefore, the correct answer is D) volcanic arcs.