Here's a problem to solve: Light waves travel faster than sound waves, so a lightning bolt can be seen before the thunder is heard. Which factor can also affect how quickly thunder is heard?

Among the 4 following options, which is the correct answer?

- A: the electrical charge of the sound waves
 
- B: the direction in which the sound waves travel
 
- C: the amount of energy released by each sound wave
 
- D: the type of material through which the sound travels
 