19. In which one of the following locations can a person hear the echo of a sound? A. At least 16.6 meters in front of the reflecting surface B. At least 33.2 meters behind the reflecting surface C. L

19. In which one of the following locations can a person hear the echo of a sound? A. At least 16.6 meters in front of the reflecting surface B. At least 33.2 meters behind the reflecting surface C. Less than 16.6 meters in front of the reflecting surface D. Less than 33.2 meters behind the reflecting surface