听力原文： Strange things happen to time when you travel, because the earth is divided into twenty-four time zones, one hour apart. You can have days with more or fewer than twenty-four hours, and weeks with more or fewer than seven days. If you make a five-day trip across the Atlantic Ocean, your ship enters a different time zone every day. As you enter each zone, the time changes one hour. Traveling west, you set your clock back traveling east, you set it ahead. Each day of your trip has either twenty-five or twenty-three hours. If you travel by ship across the Pacific, you cross the international date line. By agreement, this is the point where a new day begins. When you cross the line, you change your calendar one full day, backward or forward. Traveling east, today becomes yesterday traveling west, it is tomorrow ! Which of the following is the difference in time between zones?