按要求改写句子。
1. Did you watch videos yesterday evening? (作肯定回答)
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2. There is an Australian teacher in our school this year. (用last year改写)
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3. He did his homework an hour ago. (改为一般疑问句，并作否定回答)
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4. Ellen is going to clean the blackboard. (用often改写)
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5. He cleaned the classroom and played football that afternoon. (改为否定句)
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