Answer:
A. The Pacific plate is being subducted under the North American plate.
Step-by-step explanation:
The distribution of volcanoes among the northwest all the way up to Alaska is due to the crashing of two tectonic plates. In the northwest, one of the pacific plates, specifically the oceanic Farallon Plate is being subdued or pushed under the North American Plate. When this happens, rocks beneath the surface melt and become magma, which raises to the surface to build volcanoes.