The Transition Zone Between the Upper and Lower Mantle Is

The transition zone between the upper and lower mantle is marked by:

A) abrupt changes in material rigidity 400 kilometers and 700 kilometers below the asthenosphere.
B) abrupt changes in temperature 400 kilometers and 700 kilometers below the Earth's surface.
C) abrupt changes in mineral structure 400 kilometers and 700 kilometers below the Earth's surface.
D) abrupt changes in pressure 400 kilometers and 700 kilometers below the lithosphere.