Which is the best summary of the passage? 1. Bats calls helped early scientists understand echolocation. Scientists found that bats had trouble flying when their ears full of wax. 2. Scientists recently found that bats use sound to navigate. They named the process echolocation. Bats use to find the objects. 3. Scientists knew long ago how bats use echolocation. Later, scientists figured out how to use it to make a special Walking stick. 4. Early scientists Thought that bats use their hearing to navigate. Scientists later explained echolocation. This led to more progress,