Given the task definition and input, reply with output. In this task, you are given a paragraph, event and an entity. The event is part of the given paragraph and it changes the state of the entity. Your task is to classify the state of the entity into three classes: 1) not exist, 2) unknown location and 3) known location. "not exist" means the entity doesn't exist in that state anymore. "unknown location" means the entity exists in that state but location is unknown. "known location" means the entity exists and location is known. 

 "process paragraph : : Bats and other animals produce a high-pitched tone. The sound travels in waves, as sound does. The sound "bounces" off of a nearby object. The sound wave returns to the bat. The bat hears the echoed sound. Folds in the bat's ear and adaptations in the bat's brain enable it to determine the size, shape, and position of the other object via the properties of the returned sound waves. Other animals use echolocation in generally similar ways. ", "event : The sound travels in waves, as sound does.", "entity : high-pitched tone ; sound ; sound wave ; echoed sound" 

 unknown location 