In Most Cases, the Distance Between the Seismically Slow Upwelling

Multiple Choice

In most cases, the distance between the seismically slow upwelling zone and the closest downwelling zone is

A) much greater than the thickness of the convecting mass.
B) much less than the thickness of the convecting mass.
C) about the same as the thickness of the convecting mass.
D) about the same as the thickness of the mantle.