Strange things happen to time when you travel．because the earth is divided(劃分) into twenty．four zones(地區(qū))．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(大西洋)Ocean，your ship enters(進(jìn)入) a different time zone every day．As you enter each zone，the time changes one hour. Travelling west, you set your clocr back, travelling east, you set it ahead．Each day of your trip has twenty-five or twenty—three hours．

If you travel by ship across the Pacific(太平洋)，you cross the international date line(國(guó)際日期變更線). The world agrees that this is the point where a new day begins．When you cross the line，you change your calendar(日歷) one full day，backward(向后)or forward(向前)。Travelling east, today becomes yesterday；traveling west it is tomorrow．

根據(jù)短文內(nèi)容，回答下面的問題。

1. Why do strange things happen to time when we travel?

2. Is one hour the difference in time between zones?

3. How do you set your clock if you cross the Antlantic Ocean going west? 

4. What is the name for the point where a new day begins?

5. What will change when you cross the line?