What Is the Main Reason That Ray Paths of Seismic

What is the main reason that ray paths of seismic waves are curved like dipping arcs, rather than proceeding along the straightest, shortest path as they pass through the whole earth?

A) The earth gets too hot and the seismic waves steer away into the shallower, colder regions.
B) The rock layers themselves are bent and sagged and the waves actually travel parallel to the distorted rock layers or beds.
C) The stiffest, most brittle rocks near the surface transmit sound waves better.
D) Velocity increases with depth.