If two trains pass each other going opposite directions on parallel east-west tracks, which of the following observations provides another illustration of the effect described above? A. If the eastbound train blows its horn as they pass, passengers on the westbound train will hear a sound that decreases in pitch. B. If the eastbound train blows its horn as they pass, passengers on the westbound train will hear a sound that increases in pitch. C. If the eastbound train blows its horn as they pass, passengers on the eastbound train will hear a sound that decreases in pitch. D. If the eastbound train blows its horn as they pass, passengers on the eastbound train will hear a sound that increases in pitch. E. If the eastbound train blows its horn as they pass, passengers on the eastbound train will hear a sound that is steady in pitch.