When a train whistling passes near you, a considerable change in the pitch of the sound is heard. When the train is moving away, the pitch of the sound _ whereas the pitch of the sound _ when the train is approaching.

Explanation

The correct answer is that the pitch of the sound decreases when the train is moving away and increases when the train is approaching. This phenomenon is explained by the Doppler effect, which describes how the frequency of a wave changes relative to an observer moving in relation to the source of the wave. When the train approaches, the sound waves are compressed, resulting in a higher frequency and thus a higher pitch. Conversely, when the train moves away, the sound waves are stretched out, leading to a lower frequency and lower pitch. The other options misunderstand this effect, suggesting incorrect changes in pitch or that the pitch remains unchanged, which is not consistent with the principles of wave motion and the Doppler effect.