Trees are greatly useful to man in three very important ways.
The first important way is that they provide man with food, wood and other products. Trees provide not only man with food, 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（阴凉处）. On a hot summer day, people are looking forward to having a rest under the shade of a tree after they have walked a long way. You can imagine how important the shade of a tree is to man and to animals.
The third important way is that trees help to prevent drought（旱灾） and floods（水灾）. However, in many parts of the world, man has not realized the third important way. They cut trees down in large numbers. There will be fewer trees in the future.
People should protect trees, or they will find that they have lost the best friends they had in the end.
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Trees are useful to man in    important ways.	Trees provide man with      , wood and other products.
Trees give man shade on a   summer day.
Trees help to   drought and floods.
If people don’t protect trees, they will find they have lost     they had.