Sounds.

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Across
  1. 3. Something is vibrating.
  2. 4. Cannot speak.
  3. 6. Sound travels as a ___________?
  4. 8. Unit of volume.
  5. 11. Why we can't hear the Sun.
  6. 12. Pitch too high for humans to hear.
  7. 15. Instrument with strings.
Down
  1. 1. Sounds I don't like.
  2. 2. Low pitch instrument.
  3. 5. How fast is it vibrating?
  4. 6. High pitch instrument.
  5. 7. Cannot hear.
  6. 9. They navigate using sound.
  7. 10. Moving back and forth.
  8. 13. High or low.
  9. 14. Unit of frequency