On This Map of Earthquakes near Japan, Why Do Shallow

Multiple Choice

On this map of earthquakes near Japan, why do shallow earthquakes (yellow dots) occur to the east and deeper earthquakes (red dots) occur to the west?

A) the continental crust is thicker to the east
B) the crust is hotter near Japan, closer to the volcanoes
C) there is a continental collision to the east
D) the subduction zone dips to the west