Final answer:
Jonas thinks the music he hears at the end of the novel is only an echo because of his previous encounters with echoes in his journey.
Step-by-step explanation:
At the end of the novel, Jonas hears music coming across the distance he has traveled. He believes it is only an echo because he has previously encountered echoes in his journey. An echo is a sound wave that bounces off a surface and returns to the listener, creating the perception of a repeated sound. Jonas associates the music he hears with an echo based on his previous experiences.