Humans and animals need oxygen to exist. Without it, most living things will die. But where does oxygen come from? Trees. Trees can take in much carbon dioxide (二氧化碳) which may be bad for our environment and produce oxygen for us to breathe. |
All people know that trees are important to us. Scientists believe human life would be impossible if there were no trees on Earth. |
Trees are a major source (来源) of food. Apples, oranges, lemons all come from trees. Humans and animals knew how to get food from trees many years ago. |
In fact, many kinds of important medicine come from trees too. Some special things in trees can be used to produce medicine. Also, trees create more beautiful and relaxing environments. They help protect the soil(土壤). |