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    Mark Twain was a great American writer. He was very busy, so he often forgot something.

    One day he went to a city by train. When he was in the train, the conductor(售票员)asked him for his ticket, but he couldn't find the ticket. The conductor knew Mark Twain. She said, "Show me your ticket on your way back. If you can't find it, it doesn't matter. "

    "Oh, no," said Mark Twain. "I must find the ticket. I can't find it, how can I know where I'm going?"