When looking at a seismogram (the piece of paper that records the arrival of seismic waves), you will notice that different waves arrive at the same seismic station at different times after the event. The main reason for this is

A. Waves travel at different velocities

B. Certain waves travel through liquids and others do not 

C. The nature of the bedrock changes from the event to the seismic station 

D. P-waves are emitted from the rupture first, followed by S-waves and then surface waves E. Answers a and d only