Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

Sound is a form of
Sound is produced by
Sound transmission requires a it cannot travel in a vacuum
Echoes are sound
The human detects sound vibrations
Very sounds can cause damage to hearing
The speed of sound is than the speed of light
Because of this we see before we hear thunder