单项选择题：关于寿命周期成本分析方法局限性的表述中，不正确的是（）。A.假定项目方案不存在确定的

题型：单项选择题

The effects of rapid travel on the body are actually far more disturbing than we realize. Jet Lag is not a psychological consequence of having to readjust to a different time zone. It is due to changes in the body’s physiological regulatory mechanisms, specifically the hormonal systems, in a different environment.

Now that we understand what Jet Lag is, we can go some way to overcome it. A great number of the body’s events are scheduled to occur at a certain time of day. Naturally these have to be regulated, and there are two regulatory systems which interact.

One timing system comes from the evidence of our senses and stomachs, and the periodicity we experience when living in a particular time zone. The other belongs in our internal clocks (the major one of which may be physically located in a part of the brain called the suprachiasmatic nucleus) which, left alone, would tie the body to a 25-hour rhythm. Normally the two timers are in step, and the surroundings tend to regularize the internal clocks to the more convenient 24-hour period.

If, however, you move the whole body to a time zone which is four hours different, the two clocks will be out of step, like two alarm clocks which are normally set together, but which have been reset a few hours apart. Whereas the two clocks would normally sound their alarms together, now they ring at different times. Similarly, the body can be set for evening while the sun is rising.

In time the physiological system will reset itself, but it does take time. One easily monitored rhythm is palm sweating. A man flown to a time zone different by 10 hours will take eight days to readjust his palm sweat. Blood pressure, which is also rhythmical, takes four days to readjust.

What can we do about it? It is not feasible to wait four days until the body is used to the new time zone. Fortunately there is a short cut. It relies on two things-the power of the stomach to regulate the timing of other events, and the pharmacological actions of coffee. The basic assumptions are:

Coffee delays the body clock in the morning, and advances it at night. Coffee at mid-afternoon is neutral. Protein in meals stimulates wakefulness, while carbohydrates promote sleep. Putting food into an empty stomach helps synchronize the body clock.

46. What is jet lag associated with?

A. Psychological change. B. Physiological change.

C. Inexperience of rapid travel. D. Unfamiliar environment.

47. What helps us to adjust to a 24-hour rhythm?

A. Alarm clock. B. Suprachiasmatic nucleus in our brain.

C. Signals from outside of the body. D. Our senses and stomachs.

48. What do we know from the fifth paragraph?

A. A person moving to a different time zone will suffer from high blood pressure.

B. A person moving to a different time zone will sweat a lot.

C. Moving to a different time zone will affect both palm sweat and blood pressure.

D. If the rhythm of blood pressure and palm sweat are not in step, there will be jet lag.

49. What should we do if we want to stay awake?

A. To take coffee at three o’clock in the afternoon.

B. To have meals that contain lots of protein.

C. To have some carbohydrate drinks.

D. To stop putting food into our stomach.

50. How can we cure jet lag?

A. To sleep for days. B. To wait for self-recovery.

C. To drink tea. D. To get something to eat.

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关于寿命周期成本分析方法局限性的表述中，不正确的是（）。A.假定项目方案不存在确定的

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