If you’ve tried studying when you’re tired, you know that it can seem very impossible to do well.
A study of sleep in sparrows suggests the relationship between sleep and the ability to learn may be more complicated(复杂) than people knew.
Niels C·Rattenborg, a scientist from Wisconsin-Madison, wanted to find out how the sparrows were able to deal with getting so much less sleep. He and his team brought eight wild birds into a lab and watched them for one year. They invented a game to check how well the birds could learn. In the game, the sparrows had to peck(啄)three buttons （按钮）in a right order to get a food treat. The scientists discovered that the birds’  ability to learn the right button order depended on(依靠)two things: the time of year and the amount of sleep the birds had had.
During the migration（迁徙）season, the sparrows were restless at night and got much less sleep than usual. Even so, they were able to understand how to get the food quickly as if they’d had a regular night of sleep. Outside the migration season, they found the sparrows that got less sleep than usual had much more difficulty learning how to get the food treats than birds that had a regular sleep.
The results show that the sparrows can deal with much less sleep during the migration season than usual. If scientists can find out why, they may learn from sparrows and find ways of helping people deal with getting much less sleep. Until scientists fully understand the relationship between sleep and learning, it’s better to get plenty of sleep when preparing for an exam.
The passage is mainly about          .

A．sparrows’ migration.

B．sleep lessons from Sparrows.

C．how to get less sleep while studying

D．how sparrows that got less sleep get food treats

Why can sparrows get much less sleep during the migration season?

A．They eat more.

B．The climate is better

C．They can get food quickly

D．Scientists still don’t know the reason.

What fact does the passage lead you to believe?

A．We should sleep as little as sparrows do.

B．We should get enough sleep before an exam.

C．When tired, we should try to focus on(聚焦) our study.

D．When tired, we should check how we can sleep less than usual.