题目内容：

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 kilometres.

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 sleeping technique used by birds for finding directions. “Frigatebirds 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 one 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 us understand why lack of sleep affects humans so badly.

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

A. flying.    B. fighting.

C. sleeping.    D. thinking.

2.How do the sleeping birds find the directions?

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

B. They keep one eye connected to the awake part.

C. They pay special attention to the way.

D. They have a good sleep before they start flying.

3.What is the best title of the text?

A. A Study on Birds in Flight    B. Flying Birds’ Brain Activity

C. Birds Can Sleep in Flight    D. Sleep With Half of the Brain