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22.3 2. My younger sister can stay alone now, but she could not do it last year. 3. My best friend can play tennis now, but he could not do it a month ago. 4. Your dog can open the door itself now, but it could not do it last week. 5. I can sing very well now, but I could not do it when I was a child. 6. He can cross the river now, but he could not do it when he was younger. 7. She can run very fast now, but she could not do it two years ago.