The exam at the university.

The exam at the university. The theme of last semester, "Sound and Light".
Comes the first student. Professor asks:
- Which is faster - light or sound? Student answers:
- Light.
- Well, why?
- When I turn on the radio, at first light appears, and then the sound!
- Get out!
The audience enters the second student. The professor asks the same question.
Answer: - Sound.
- Explain!
- When I turn on the TV, first appears sound, and then the picture.
- Won !!!
The professor thought: "Either the students very much stupid, and I ask very difficult questions? »
It appears the third student. Professor asks:
- You're standing on the mountain. On the opposite hill is a cannon. From her shoot. What do you fix first - a flame from the barrel, or the roar of a shot?
- Of course, the flame from the barrel!
Professor with relief asks:
- How can this be explained?
The student thought for a moment and replies:
- In front of the eyes of a lot of ears!