12.) When the automobile moves away from the listener, its horn seems __pitched. A. high B. low C. medium D. normal 13.) The changed pitch of the Doppler effect is due to changes in wave A. amplitude B. frequency C. speed D. wavelength 14. Which of the following statements is TRUE about Doppler Effect? A. It occurs when a wave source moves towards an observer. B. It occurs when an observer moves towards a wave source. C. It occurs when a wave source moves away from an observer. D. It occurs when an observer moves away from a wave source. 15. Why does the amplitude of a sound wave decrease with distance from its source? A. The amplitude of a sound wave decreases with distance from its source, because the speed of the sound wave decreases. B. The amplitude of a sound wave decreases with distance from its source, because the frequency of the sound wave decreases. C. The amplitude of a sound wave decreases with distance from its source, because the wavelength of the sound wave increases. D. The amplitude of a sound wave decreases with distance from its source, because the energy of the wave is spread over a larger and larger area