2 Look, think and complete the text with your own ideas using these words and word combinations: useful, colourful, fresh air, clean, oxygen, to give, to cut down, should shouldn't, protect, to help, to plant, to lose homes, bush, bushy, etc. Plants are good and useful for our They make our world colourful. Trees oxygen boxes for us. They clean the air give us fresh air to breathe. We should plus a lot of trees. Humans can change the Planet Earth in both positive and negative ways. First, people can cut down millions of trees.