Tom went to see his grandparents with his father. In the train Tom often put his head out of the window. His father said, "Tom, don't put your head out of the window." But Tom went on putting his head out of the window. His father took Tom's hat quietly and hid it behind his back and said to Tom, "You see your hat is gone." Tom was afraid. His father said, "Well, whistle once. Maybe your hat will come back." Tom whistled. His father put his hat on Tom's head quickly. "Oh! It's wonderful!" Tom laughed and said. He quickly took his father's hat and threw it out of the window. "Now it's your turn to whistle, Dad!" he said happily. Tom went to see his grandparents with his father   _  .
by bus by train by plane by ship