The Asthenosphere Is Considered the Low- Velocity Zone Because

The asthenosphere is considered the low- velocity zone because:

A) seismic waves travel more slowly through it than through any other region in the Earth's interior.
B) seismic waves travel more slowly through it than through other parts of the mantle.
C) in this thin layer of mantle, P- wave velocity is slower than in the crust.
D) circulation of material within asthenosphere convection currents moves extremely slowly.