Answer:
c. Sound travels slower than light.
Step-by-step explanation:
We see any thing because of the light emitted or reflected by it. Whereas the sound is carried by the sound waves. The speed of light is more than the speed of sound. This is the reason the family saw the fireworks first and then heard the sound.
The same can be experienced during the sighting of a Jet plane or a rocket where, we see them way before we can hear the roaring sound of its engines.