根据要求改写句子
1. Leave rubbish on the playground. (改为否定句)
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2. Listen to the bird, please. (改为否定句)
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3. They enjoyed themselves in the park. (保持句子意思不变)
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4. There are some rules in our school. (保持句子意思不变)
We ________ ________ ________ in our school.