Inference

[BTGmoderatorRO]

The "Doppler effect" refers to the universally perceived change in the apparent pitch of a sound when that sound is approaching or receding from the listener. Specifically, whenever the distance between the listener and the source of the sound is decreasing, the sound will be perceived by the listener as higher than its true pitch; whenever that distance is increasing, the sound will be perceived by the listener as lower than its true pitch. If the distance between the listener and the source is not changing, the listener will perceive the true pitch of the sound.

If the above principle holds, which of the following should be observed as an eastward-traveling train is approached by a westward-traveling train that is blowing its horn?
(A) Passengers in the eastbound train should hear the true pitch of the horn; passengers in the westbound train will hear a sound lower than the true pitch.
(B) Passengers in the westbound train should hear the true pitch of the horn; passengers in the eastbound train will hear a sound lower than the true pitch.
(C) Passengers in the eastbound train should hear the true pitch of the horn; passengers in the westbound train will hear a sound higher than the true pitch.
(D) Passengers in the westbound train should hear the true pitch of the horn; passengers in the eastbound train will hear a sound higher than the true pitch.
(E) Passengers in both trains should hear a sound that is higher than the true pitch.
OA is d
which of the following option is the best fit for this question? Experts, please help me with this.
Thanks you

[EconomistGMATTutor]

This is an inference question. Given all the evidence, what must be true about an eastward-traveling train that is approached by a westward-traveling train that is blowing its horn?

The evidence: Whenever distance between the listener and the source of the sound decreases, the sound seems higher; whenever that distance increases, the sound seems lower. If the distance doesn't change, the listener will perceive the true pitch of the sound.

As the horn-blowing eastbound train approaches the westbound train, the distance between the horn and the westbound passengers decreases. For them, the pitch will seem higher. However the people on the horn-blowing eastbound train are not getting any closer or farther from the horn. They will perceive the true pitch. This is what choice D says.

I'm available for further questions.