The teacher can ask his students that in waiting room at the railway station when they listen to the broadcast about which train they will take, the destination, the arrival time, and the starting time, they are whether or not as careful and serious as they listen to the infomation of all trains. If not, how do they listen to. the students ususally answer that when they hear the train they will take,they will concentrate on it, and do not care the departure time and the starting time of the other the trains. The teacher can ask his students that in waiting room at the railway station when they listen to the broadcast about which train they will take, the destination, the arrival time, and the starting time, they are whether or not as careful and serious as they listen to the infomation of all trains. If not, how do they listen to. the students ususally answer that when they hear the train they will take,they will concentrate on it, and do not care the departure time and the starting time of the other the trains.