【单选题】Most earthquakes occur within the upper 15 miles of the earth's surface. But earthquakes can and do occur at all depths to about 460 miles. Their number decreases as the depth increases. At about 460 ...
A.
The number of earthquakes is closely related to depth.
B.
Roughly the number of earthquakes varies much every year.
C.
Earthquakes are most likely to occur within the upper 15 miles of the earth's surface.
D.
Earthquakes are most likely to occur near the surfaces.