Ответ:
1. Pollution is when we make nature dirty.
2. Air pollution is caused by smoke from factories and cars.
3. Dirty air is dangerous for our bodies, especially our lungs.
4.We need trees to clean the dirty air.
5.Water pollution is caused when rubbish enter the lake and the sea.
6. Water pollution can cause fish to die and can poison our bodies, making us very thick.
7. Land pollution is caused when we throw rubbish on to the ground.
8. To protect our environment, we need to stop pollution.
9. People must stop cutting down forests and plant new trees.
10. Instead of throwing rubbish away, we should recycle it.
В самом задании не хватает еще одного слова. В 9 предложении, я предположу, что не хватает слова forests.