Birds that are half-asleep—with one brain hemisphere alert and the other sleeping—control which side of the brain remains awake, according to a new study of sleeping ducks.

　 Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemisphere’s eye stays open and alert. Birds also can sleep with both hemispheres resting at once.

　 Decades of studies of bird groups led researchers to predict extra alertness in the end-of-the-row sleepers which tend to be attacked more easily. Sure enough, the end birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction.

　 Also, birds napping at the end of the line depend on single-hemisphere sleep, rather than total relaxation, more often than inner ducks did. Turning 16 birds through the positions in a four-duck row, the researchers found that compared with 12 percent for birds in internal spots, outer birds half-asleep during some 32 percent of napping time.

　 “We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness at the same time in different regions of the brain,” the researchers say.

　 The results provide the best evidence for a long-standing assumption that single-hemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. He’s seen it in a pair of birds napping side-by-side in the zoo and in a single pet bird sleeping by a mirror. The mirror-side eye closed as if the reflection were a companion and the other eye stayed open.

　Useful as half-sleeping might be, it’s only been found in birds and such water animals as dolphins, whales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning.

　 Studies of birds may offer unique insights into sleep. Jerome M. Siegel of the UCLA says he wonders if birds’ half-brain sleep “is just the tip of the iceberg.” He supposes that more examples may turn up when we take a closer look at other species.

77. According to the passage, birds often half sleep because ______.

　　　 A. they have to watch out for possible attacks

　　　 B. their brain hemispheres take turns to rest

　　　 C. the two halves of their brain are differently structured

　　　 D. they have to constantly keep an eye on their companions

78. What is implied about the example of a bird’s sleeping in front of a mirror?

　　　 A. An imagined companion gives the bird a sense of security.

　　　 B. Birds prefer to sleep in pairs to amuse themselves.

　　　 C. The phenomenon of birds napping in pairs is widespread.

D. A single pet bird enjoys seeing its own reflection in the mirror.

79. While sleeping, some water animals tend to keep half awake in order to ______.

A. alert themselves to the approaching enemy

　　　 B. emerge from water now and then to breathe

　　　 C. be sensitive to the ever-changing environment

　　　 D. avoid being swept away by rapid currents

80. By saying “just the tip of the iceberg”, Siegel suggests that ______.

　　　 A. half-brain sleep has something to do with icy weather

　　　 B. the mystery of half-brain sleep is close to being solved

　　　 C. most birds living in cold regions tend to be half sleepers

D. half-brain sleep may exist among other species

　　From the very beginning, Martin felt that he was bound up with（与……紧紧地在一起）his lovely little patient. One day, following some tests , Betty gave the doctor a big hug（拥抱）.

　　A few months later the doctor removed not only the tumour（肿瘤）, but also the entire lower left side of Betty’s gum（牙龈）and jawbone. Because Betty was so young, Martin was hopeful that her jawbone might regenerate.

　　Within three months, Betty’s tumour grew as large as an orange, changing the natural appearance of the left side of her small, delicate （ = thin; not strong）face. Soon she couldn’t even close her mouth, and as her eating problems worsened, Betty ‘s weight dropped from 20 kilos to 15. Martin knew from experience that it might invade the brain.

　　The only other possibility was thorough radiation therapy （放射疗法）. Night after night, Betty's father gave her injection, but the tumour remained as big as ever. Then one evening. Morgan noticed that the tumour had begun to change. It was actually becoming smaller! For two months her tumour appeared to be going away for ever. In the coming months, Betty’s tumour continued to appear. She was able to eat solid food once again. Her jawbone was regenerating. The tumour was gone.

　　67．What do you think the underlined word regenerate means? It means “________”.

　　A. lose one’s life

　　B. give a new life to

　　C. be made by hand

　　D. pass on from one generation to another

　　68．If Betty’s jawbone didn’t regenerate, the doctors ________ .

　　A. would rebuild her jaw

　　B. would continue the treatment

　　C. would use new medicine

　　D. could do nothing else

　　69．If the brain should be invaded, the result would ________.

　　A. prevent her growth

　　B. reduce her weight

　　C. cause her brain damaged

　　D. affect her eyesight

　　70．What did the doctors do two months later?

　　A. They continued their observations.

　　B. They gave up the operation on Betty.

　　C. They found out what caused Betty’s strange disease.

D. They declared that Betty’s strange disease was cured.

 “But what if I break my arm again？”My five-year-old daughter asked,looking very　1　.I knew she　2　very much to learn to ride,but ever since she’d fallen off her bike and broken her arm,she’d been afraid.

“Oh,honey,”I said.“I don’t think you’ll break another arm.”“　3　I could,couldn’t I？”“You know,honey,”I said,“　4　everything you do comes with risks.You could get a broken arm in a car　5　and then be afraid to　6　ride in a car again.You could break your arm jumping a rope.You could break your arm at gym.Do you want to　7　going to gym？”“No,”she said.And with a determined spirit,she stood up and　8　to try again.

I spent the rest of the afternoon at the park watching a very　9　little girl overcome a fear,and　10　myself on being a useful single parent after a painful divorce(离婚)．

As we walked home,she asked me about a conversation she’d overheard me having with my　11　the night before.

“Grandma wanted you to find someone to　12　.”“What grandma wants is for someone to　13　my heart again.”“But Mom...”“You’re too young to　14　it,”I told her.“So I guess love isn’t like a broken arm.”she said. 　15　to answer,we walked the rest of the way in　16　.When I got home,I called my mother and　17　her for talking about this to my daughter.Then I did what I’d seen my brave little girl do that very afternoon.I agreed to　18　Steve.

Steve was the man for me.We　19　less than a year later.It turned out my mother and  daughter were　20　.

1．A.surprised             B．disappointed            C．sad                       D．puzzled

2．A.wanted                B．hated                     C．lost                       D．gained

3．A.And                   B．Or                        C．Instead                  D．But

4．A.Almost                B．Hardly                    C．Nearly                   D．Mostly

5．A.trade                    B．sale                        C．accident                  D．show

6．A.ever                    B．never                     C．even                     D．yet

7．A.start                    B．regret                     C．finish                     D．stop

8．A.offered                B．agreed                   C．had                       D．chose

9．A.shy                    B．weak                     C．brave                     D．gentle

10．A.congratulating     B．praising                   C．encouraging           D．celebrating

11．A.father                 B．mother                  C．sister                    D．brother

12．A.like                    B．know                     C．love                     D．teach

13．A.warm                B．feel                       C．buy                      D．break

14．A.understand         B．believe                    C．accept                  D．receive

15．A.Unable               B．Unwilling                C．Uncertain               D．Unhappy

16．A.excitement          B．sorrow                   C．silence                   D．surprise

17．A.punished            B．scolded                   C．thanked                 D．appreciated

18．A.hire                  B．meet                     C．fire                      D．invite

19．A.left                   B．married                   C．moved                  D．quarrelled

20．A.wrong              B．right                       C．clear                     D．clever