Why Did the Visigoths and Other Germanic Peoples Migrate Westward

Why did the Visigoths and other Germanic peoples migrate westward?

A) Nomadic steppe people of Central Asia, such as the Huns, were pressuring them from the east.
B) Superior agricultural lands in western Europe attracted the Germanic people as they adopted settled agriculture.
C) The retreat of Roman forces from these areas created a political vacuum that the Germanic people moved to fill.
D) Exceptionally cold decades in the mid-third century forced the Germanic peoples to seek more favorable climates for agriculture.