第一节：完形填空（共15小题，每小题1.5分，满分22.5分）
阅读下面短文，掌握其大意，然后从21—30各题所给的四个选项（A、B、C和D）中，选出最佳选项，并在答题卡上将该项涂黑。
Japanese high school students do not drive cars. Many either walk or ride bicycles if distance is not too great. In other cases, a lot of students must 21 public buses and trains, often changing lines several times in order to reach their 22 .