Which of the following descriptions of the behavior of seismic waves is NOT correct?
a. When seismic waves pass through the boundary between two media, the waves tend to change speed and bend, or refract, in several directions.
b. When seismic waves approach the boundary between two media at a relatively small angle, they may bounce, or reflect, off the surface.
c. Within the Earth, seismic wave speed tends to increase with depth.
d. Changes in material, temperature, pressure, and physical state can all affect the speed of a seismic wave.