题目内容：

Everyone experiences tiredness at work sometimes. At some point (usually around 2:00 pm), you find yourself ready for a nap (打盹). Your energy changes naturally throughout the day. Productivity expert Chris Bailey examined this motivation, focus and energy levels for 21 days and found that all three tend to spike between 7:00 and 8:00 am, 11:00 and 12:00pm, and 6:00 and 7:00 pm. In addition to all those highs, he also noticed time when focus, energy, and motivation were nowhere to be found. Chris was tired at work.

Your peak time productivity time may be different from Mr. Bailey’s, but the overall shape of your energetic graph would still look like a series of zigzags (锯齿). The amount of sleep you have, the food you eat, and how you exercise are a few of the factors that cause rises and falls in your energy level.

We can fill up on coffee and sugar as much as we want, but we are fighting a natural downturn in energy when we do this. Your tiredness may seem like an inconvenience, but it’s really your body tell you that it needs rest.

Our bodies operate on a natural clock called circadian rhythm(生理节律). This sleep/wake cycle is perfectly adapted to give us enough sleep over the course of a 24-hour period. Natural light is the primary means that your body uses to assess whether or not you should be asleep.

Therefore, circadian rhythms do not agree with the average 9-5 job. Irregular sleep schedules, the light from electronic devices, and natural light exposure for a long time can also affect the cycle. This is why people working the graveyard shift have an increased risk for developing health problems. They must remain awake when their body tells them it’s time for bed, and their sleep constantly disrupted when they try to stay awake on days off.

1.Which of the factors does not contribute to the differences of the peak of productivity time according to the author?

A. Diet    B. Sleep

C. Exercise    D. Character

2.Why do people fail to work energetically for eight hours according to the author?

A. Because our body assesses our needs for sleep according to natural light.

B. Because the light from electronic devices stops them from concentrating on their jobs.

C. Because most people choose to stay up late at night for recreational activities.

D. Because of the stress from their jobs and busy schedule that they can not cope with.

3.Who is likely to develop sleeping problems according to the passage?

A. A manager who needs to travel a lot.

B. An athlete who trains hard for champions.

C. A guard who has to work in a museum at night.

D. A bus driver who drives from 6 am. to 1 pm.

4.What does the passage mainly tell us?

A. The reasons for sleeping problems.

B. People have downturns when they work for natural causes.

C. How people can fight against the low energy levels when they work.

D. How to develop healthy sleeping habits.