填词
One day,the American w_____ Mark twin went to a city b____ train.He wanted to see a friend of h___.he was a very busy man and he often f____ something.
when he was in the train ,the conductor asked him to show his t____ .mark twin looked for it here and there ,but he c___ find it.The condoctor k___ him.so she said ,"S_____ me your ticket on your way b____home .and if you can't find it ,it doesn't matter." "Oh ,but it does ."said Mark Twin ."I must find it .if I can 't find it ,how can I know w____ I'm going ."