Answer:
Explanation: The correct answer is: the sound of the train's horn to appear to be at a higher pitch.
As the high speed rail train approaches the crossing, it moves towards the sound waves it creates. This causes the frequency of the sound waves to be compressed, which results in an apparent increase in frequency or pitch of the train's horn. This effect is known as the Doppler shift. Therefore, the sound of the train's horn will appear to be at a higher pitch.