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Birds have been observed to sleep while in flight for the first time ever. Because of some flights that can often last several days, weeks, or even longer, some sea birds have long been thought of being able to fall fully asleep while “on the wing”, though it was not proven.

Now, researchers say they have evidence which shows birds can sleep in flight. Scientists from Max Planck Institute used a sample of 15 adult female frigate birds(军舰鸟) to test the sleep patterns. Each bird had a small electroencephalogram (EEG脑电图) sensor fitted to record changes in the animals’ brain activity as they flew for up to 10 days and over 3,000 km.

The readings showed that during flight the birds could sleep using one hemisphere of the brain, or both together. It was known that frigate birds could sleep with one “half” of the brain, which allows them to keep one eye open and “connected” to the awake half.

According to the research, it is a sleeping technique used by birds for finding directions. “Frigate birds sleep mostly while circling in rising air and keep the eye connected to the awake hemisphere facing the direction of flight, suggesting that they watch where they are going,” says the study.

Despite the ability to fall “fully” asleep, the birds were found to do it less in the air compared to on land. They slept “very little and less deeply” while in flight. This suggests that though it is possible, falling totally asleep is not very good during flight which will need the bird’s attention.

The researchers said the short sleep could be serving as “power naps” to keep the birds going until they return to land. Further study could help our understanding why lack of sleep affects humans so badly and in such a “rapid” manner.

1.The phrase “on the wing” in the first paragraph may mean ______.

A sleeping

B fighting

C flying

D thinking

解析：选C。词义猜测题。从文章第一段第一句Birds have been observed to sleep while in flight for the first time ever.可以得知有的鸟在飞行中睡觉从，该句前半部分的fall fully asleep可以得知小鸟在飞行的时候会睡着，使用on the wing的意思为“飞行”。

2.Why did the researchers fit the frigate birds with EEG sensor?

A They wanted to know animals’ brain activity.

B They wanted to get some of the good samples.

C They wanted to help the birds fly much longer.

D They wanted to use the birds to find directions.

解析：选A。细节理解题。根据第二段最后一句record changes in the animals’ brain activity可知安装脑电图是为了记录鸟的大脑的活动。

3.When the frigate birds sleep with one half of the brain, they ______.

A should keep both eyes open

B could use only one of the eyes

C needn’t keep their brain awake

D have to stop to eat something

解析：选B。细节理解题。根据第三段最后一句which allows them to keep one eye open可以得知小鸟在飞翔的时候可以闭着一只眼睛。

4.How do the sleeping birds find the directions?

A They keep their eyes connected to the awake part.

B They sleep less when they are circling in rising air.

C They pay special attention to the way they travel.

D They have a good sleep before they start flying.

解析：选A。细节理解题。根据第四段第二句keep the eye connected to the awake hemisphere facing the direction of flight可以得知保持部分大脑的清醒来判断方向。