单选题 Do you ever feel sick, confused, or very tired after a long plane ride? If you were fly-ing east to west or west to east, the problem could have been jet lag. (45) Jet lag happens when your body's time clock becomes confused. Crossing several time zones may make you feel very tired. You may become confused because you are tired. In fact, you may become so confused that you won't be able to do your work. You might get headaches and feel that you have problems eating and sleeping. These are all symptoms of jet lag.
However, if you feel tired after flying from north to south or south to north, you do not have jet lag. Maybe you feel tired from the tiredness and work of getting ready for the trip. You will feel better after you get some sleep. The symptoms that you feel during a flight, such as thirst and motion sickness, are not jet lag either. They are caused by the air pressure in the plane. When you travel north or south, you do not cross time zones. So you do not have true jet lag.

单选题 What is jet lag?
A. The tired and confused feeling that you get after flying.
B. Being unable to catch the plane.
C. Being too heavy to be on the plane.
D. Losing the clock in your body.

单选题 Flying in which direction is more likely to cause jet lag?
A. North to south. B. South to north.
C. West to east. D. None of the above.

单选题 Which of the following is NOT a symptom of jet lag?
A. Eating problems. B. Motion sickness.
C. Headaches. D. Sleeping problems.

单选题 If you are tired when you fly south or north,
A. you will feel better after some sleep
B. you should go to see a doctor
C. you should do some exercise
D. you should eat more

单选题 Which of the following is true according to the passage?
A. All people can still work very well after the flight from China to America.
B. If you feel thirsty during a flight, you have jet lag.
C. Your body clock may get confused when you cross time zones.
D. You will have jet lag if you fly from Japan to Sydney