Trees are useful to man in three important ways.
The first important way is that they provide man with wood and other products. Trees provide not only man but also many animals with food. Without trees, many animals could not live on the Earth. It's not easy for man to live on the Earth either.
The second important way is that trees give us shade. On a hot summer day, people are eager（渴望）to have a rest under the tree after they have a long walk. You can imagine how important the shade of a tree is to man and animals.
The third important way is that trees help to prevent droughts and floods. However, in many parts of the world, people haven't realized the third way. They cut trees down in large numbers. In the end, they find that they have lost the best friends they had.
