Mr Brown likes to be exact (确切的). One day when he took a walk in the street , a man came up and asked him the way to the bookshop . He said to him , "Cross the bridge (过桥) and turn to the right . "The man asked again , "Is the bridge very long ? ""Only thirty metres long . " The man thanked him and went to the bridge . Suddenly he heard a man running after him . "Stop ! "Mr Brown said to the man . "I'm sorry . I forget the bridge is forty metres long . If you walk thirty metres long and turn to the right , you will fall into the river . " 根据短文内容,判断下列句子的正 误 。