The change in pitch of a train's horn as it passes while you are standing still can be explained by
a. resonance.
b. the doppler effect.
c. sympathetic vibration.
d. ultrasonic vibrations.

B. the Doppler effect.

The Doppler effect is a phenomenon whereby the frequency from a moving object towards an observer appears to increase while the frequency appears to decrease as it moves away from the observer.

Neptune is the eighth planet from the sun. it was the first planet to get its existence predicted by  mathematical calculations  before it was actually seen through a telescope on sept. 23, 1846. irregularities in the orbit of  uranus  led french astronomer alexis bouvard to suggest that the gravitational pull from another celestial body might be responsible. german astronomer johann galle then relied on subsequent calculations to   spot neptune via telescope. previously, astronomer galileo galilei sketched the planet, but he mistook it for a star due to its slow motion. in accordance with all the other planets seen in the sky, this new world was given a name from greek and roman mythology — neptune, the roman god of the sea.