请按要求改写句子。
1. My sister rowed a boat last Saturday. (对画线部分提问)
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2. I played football yesterday afternoon. (改为一般疑问句并作否定回答)
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3. They bought some flowers for their teachers last Wednesday. (变成否定句)
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4. Mary wrote a letter to me last week. (对画线部分提问)
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