Many travelers face a common problem： jet lag. Scientists define jet lag as the effect on the human body of traveling across time zones.

Sofia Axelrod studies circadian（晝夜）rhythms at Rockefeller University in New York. She said a circadian rhythm is like a biological clock programmed into almost every cell in the body.” The clock is set by the 24-hour light and dark pattern，” Axelrod said. “Every morning when we wake up， specialized receptor cells in our retina receive a daylight signal， which is transmitted to the brain and from there， （to） the whole body.”

When we travel to another time zone， our eyes do not receive the daylight signal at the usual time. This causes our “internal clocks” to reset. But that process can take a while. During that period， we feel the effects of jet lag.

Malcolm von Schantz is a professor specializing in circadian rhythms in England. He said paying a lot for a bigger seat and more space in an airplane can prevent sleep deprivation. He also said timing your flights can help. For example， he suggests flying from Europe to North America during the day， so that it is evening when passengers land and they can get to sleep.

Experts say being in sunlight is important to resetting your internal body clock. That could mean either avoiding morning sun or seeking it out， depending on where you started. Getting light in the morning will move your body clock forward， while light exposure in the early evening will delay it. Sleeping for a short time during the day is acceptable， but scientists warn against sleeping for longer periods later in the day. Doing so might make it harder to sleep through the night.

Russell Foster of Oxford University suggests business travelers consider arriving a day or two ahead of any important meetings or events to avoid unwise decisions and unpleasant emotions. While tourists needn’t think as clearly as business travelers， he still advises tourists to get enough sleep before doing anything that might be risky or that requires a lot of attention， like driving.

（材料選自VOA，有刪改）

1.What’s the function of the first paragraph？

A. To introduce the topic.

B. To summarize the passage.

C. To arouse the readers’ interest.

D. To give background information.

2.Why is the example of flying from Europe to North America mentioned in paragraph 4？

A. To tell us good sleep is very useful.

B. To prove timing your flights is helpful.

C. To show taking a flight is a wise choice.

D. To show the ticket is cheaper in the daytime.

3. What is the main idea of the last three paragraphs？

A. How to sleep well.

B. How to reset biological clock.

C. How to have a trip happily.

D. How to prevent jet lag.

4. Who is unlikely to suffer from jet lag？

A. A tourist flying from England to America at night.

B. A tourist travelling around all day without any rest.

C. A business traveler getting to an important meeting on time.

D. A tourist keeping having a nap after lunch when travelling.

1.A。解析：推理判斷題。材料第一段先是提出很多游客面臨時(shí)差問(wèn)題，然后提出科學(xué)家對(duì)時(shí)差的定義，由此引出話題——如何在旅行中預(yù)防時(shí)差反應(yīng)，故選A。

2. B。解析：推理判斷題。材料第四段的第三句提到“他還說(shuō)，安排航班時(shí)間會(huì)有所幫助”，由此可知安排好航班時(shí)間會(huì)對(duì)預(yù)防時(shí)差反應(yīng)有幫助，故選B。

3.D。解析：主旨大意題。材料第四段主要講述Malcolm von Schantz在旅行中如何預(yù)防睡眠被剝奪，材料第五段主要講述專家們對(duì)重設(shè)生物鐘的建議，材料第六段主要講述牛津大學(xué)的Russell Foster對(duì)商務(wù)旅行者和普通旅行者的建議。綜合起來(lái)看，這三段講述的是如何預(yù)防時(shí)差反應(yīng)，故選D。

4.D。解析：細(xì)節(jié)理解題。材料第四段的最后一句提到“他建議白天從歐洲飛往北美”，由此可以排除A選項(xiàng)。材料最后一段的第一句提到“牛津大學(xué)的Russell Foster建議商務(wù)旅行者考慮在任何重要會(huì)議或活動(dòng)前一兩天到達(dá)”，由此可以排除C選項(xiàng)。材料第五段的第四句提到“白天短時(shí)間睡眠是可以接受的”，由此既可以排除B選項(xiàng)，也可以確定D選項(xiàng)是正確的。