5. How do sponges try to protect themselves against harm from the environment? Is that method efficient or rudimentary?
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!