Strange things happen to time when you travel, because the earth is divided into twenty-four time zones, and one hour separate. 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, yon 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. When you cross the Atlantic Ocean traveling west, you should set clock ______.

A. back one hour in each new time zone
B. back one hour for the whole trip
C. ahead one hour in each new time zone
D. ahead one hour for the whole trip