The “Doppler effect” describes the change in the perceived pitch of a sound as the source of the sound moves relative to an observer. When the distance between the observer and the sound source decreases, the pitch is perceived as higher; when the distance increases, the pitch is perceived as lower. If a northbound train is approaching a southbound train that is sounding its horn, which of the following statements is correct? (A) Passengers in the northbound train will hear the true pitch of the horn; passengers in the southbound train will hear a sound lower than the true pitch. (B) Passengers in the southbound train will hear the true pitch of the horn; passengers in the northbound train will hear a sound lower than the true pitch. (C) Passengers in the northbound train will hear the true pitch of the horn; passengers in the southbound train will hear a sound higher than the true pitch. (D) Passengers in the southbound train will hear the true pitch of the horn; passengers in the northbound train will hear a sound higher than the true pitch. (E) Passengers in both trains will hear a sound that is higher than the true pitch.