试题：
| 用所给单词的适当形式填空 |
| 1. Trees must __________(prevent) from being cut down. 2. They __________(plant) ten thousand trees by last spring. 3. The sheep __________(tie) to the tree has eaten a lot of grass. 4. I can easily hear combs __________(go) through hair. 5. Great changes __________(take) in our hometown in the last ten years. |
答案：
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