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 to be 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（抽樣） of 15 adult female frigate birds to test the sleep patterns.Each bird had a small electroencephalogram（EEG） sensor（傳感器） fitted to record changes in the animals brain activity as they flew for up to 10 days and over 3，000 kilometers.
   The readings showed that during flight the birds could sleep using one hemisphere（半球）of the brain，or both together.It was known that the 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 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 birds 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 us understand why lack of sleep affects humans so badly.

（1）Why did the researchers fit the frigate birds with EEG sensors？

To record changes in the animals brain activity as they flew for up to 10 days and over 3，000 kilometers.

To record changes in the animals brain activity as they flew for up to 10 days and over 3，000 kilometers.

（2）How could the frigate birds sleep during flight？

They could sleep with one "half" of the brain.

They could sleep with one "half" of the brain.

（3）How do the sleeping birds find the direction？

They keep one eye open and "connected" to the awake half.

They keep one eye open and "connected" to the awake half.

（4）What could the short sleep serve as for the birds？

It can keep the birds going until they return to land.

It can keep the birds going until they return to land.

（5）What can be the best title for the text？

A Study on Birds Seeping in Flight

A Study on Birds Seeping in Flight