The following picture shows the three primary types of plate boundaries. Which boundary is being shown in label A? an arrow pointing from A to a formation of trenches and Island Arcs, an arrow pointing from B and C to an Oceanic Spreading Ridge, and an arrow pointing from D to a trench. © 2016 US Department of the Interior; US Geological Survey Divergent boundary zones Convergent boundary zones Plate boundary zones Transform boundary zones

The label A corresponds to Convergent boundary zones  

Explanation:  

When two oceanic plates collide, it occurs oceanic convergence. The thicker and older plate subduces under the other plate, and at this point, it starts the volcanic activity. As the thicker plate descends, it is heated and melted and its materials are incorporated into the mantle. The fast subduction originates magma that ascends to the surface by crevices. This makes place to the formation of grouped volcanic islands, the island arches. Subduction zones coincide with deep-sea trenches or depressions in the ocean bed. The volcanic islands are arranged in a circumference arch shape, which is bordered by a fossa. Most of these are located in the western Pacific, where the pacific crust is older and thicker, and hence it submerges easier in the mantle.