You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each 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
(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
C