Travelling ____ today becomes yesterday; travelling west it is tomorrow.
   A. south     B. east      C. north     D. west

　　Your watch always tells you what time it is now, but strange things happen 1 time when you travel, 2 it is divided 3 twenty-four time 4 , one hour 5 .

　　You can have days with more or 6 than twenty-four hours, and weeks with more or less than 7 days.

　　If you 8 a five-day trip 9 the Atlantic Ocean, your ship enters a different time zone every day. As you enter each zone, the time changes 10 . Travelling 11 , you set your watch back; travelling east, you set it 12 . Each day of your trip has 13 twenty-five or twenty-three hours. If you travel 14 ship across the Pacific, you cross the international dateline. 15 agreement, this is 16 a new day begins. When you 17 the line, you change your calendar one full day, 18 or forward. Travelling 19 , today becomes yesterday; travelling west, it is 20 .

1．

[　　]

2．

[　　]

3．

[　　]

4．

[　　]

5．

[　　]

6．

[　　]

7．

[　　]

8．

[　　]

9．

[　　]

10．

[　　]

11．

[　　]

12．

[　　]

13．

[　　]

14．

[　　]

15．

[　　]

16．

[　　]

17．

[　　]

18．

[　　]

19．

[　　]

20．

[　　]