Question: In a deep valley on Earth, a person shouting will hear an echo as the sound is reflected back off the surrounding mountains. In a similar valley on the Moon, no echo will be heard. This is because

  Options: 
 A. the gravitational pull on the Moon is too low
 B. the temperature on the Moon is too low
 C. there is no air on the Moon for the sound to travel through
 D. the mountains on the Moon cannot reflect sound
Answer: C