The two processes that are most responsible for the decrease in the height of the Appalachian Mountains include weathering anderosion.The statement that explains why earthquakes occur more frequently in California than in Massachusetts is due to the fact that California is located on the boundary of two crustal plates, but Massachusetts is not.The feature that forms when an oceanic plate has been moving over a hot spot for millions of years is that volcanoes form as lava erupts through the oceanic plate.It should be noted that erosion and weathering reduce the height of rocks and this can lead to a decrease in the height of the Appalachian Mountains.In conclusion, the correct options are A, B, and A.