Few Earthquakes Are Recorded at Depths Below 450 Miles Because

Few earthquakes are recorded at depths below 450 miles because:

A) they are too deep within the Earth to be detected by seismographs.
B) brittle failure does not occur at depths below 200 miles.
C) slabs that descend that far have been heated sufficiently to deform plastically.
D) lithostatic pressure at these depths prevents rocks from shifting relative to each other.