Seismic Waves Travel in a Straight Line with Constant Velocity

Seismic waves travel in a straight line with constant velocity only when moving:

A) in a homogeneous medium at different temperatures and pressures.
B) in a homogenous medium at different temperatures but constant pressures.
C) in a homogenous medium at constant temperatures and pressures.
D) through media of various compositions at different temperatures and pressures.