Mark Twain（马克·吐温）was an American writer（作家）.One day he went to a city by train.He wanted to see one of his friends there.He was a very busy man.He usually forgot something. When he was in the train,the conductor（列车员）asked him for his ticket.Mark Twain looked for the ticket here and there,but he couldn't find it.The conductor knew Mark Twain.She said,“Show me your ticket on your way back.And if you can't find it,it doesn't matter.” “Oh,but it does,”said Mark Twain.“I must find the ticket.If I can't find it,how can I know where I'm going?” ( ) Mark Twain couldn't find his ticket,so he bought another one.