A、You hear the gun before you see the smoke. B、You see the smoke before you hear the gun. C、The sound of the gun will reach you

Light travels at a speed that is about a million times faster than the speed of sound. In one second, light travels about 300, 000 km, but sound travels only about 334 meters. You can get some idea of this difference by watching the start of a race. If you stand some distance away from the starter, you can see smoke come from his gun before the sound reaches your ears.
    This great speed of light produces some strange facts. Sunlight takes about 8 minutes to reach us. If you look at the light of the moon tonight, remember that the light rays left the moon 1.3 seconds before they reached you. The nearest star is so far away that the light that you can see from it tonight started to travel towards you about four years ago at a speed of nearly 20 million km per minute. In some cases, the light from one of tonight’s stars started on its journey to you before you were born.     Thus, if we want to be honest, we cannot say, "the stars are shining tonight.” We have to say, "the tars look pretty. They were shining four years ago, but their light has only just reached the earth."