Birds are warm blooded animals.though their feathers help to keep them warm ,some birds such as ducks,46.(  )(goose),and swans still can't endure harsh winter temperatures .for these reasons ,birdseed from cold climates fly to warmer climates 47.()the winter .this seasonal movement of birdseed is called migration .birds migrate to warmer places ,often hundreds of milestone away ,where they can have the best chance of 48.sur(    ).
  Birds migrate naturally .certain clues form the environment cause hormone changes in the bird's body .as the days get 49.(  )(short),for example ,these hormones tell the bird's body to store fat .this is because migrating Takes (  )energy .birds don't have a lot of time to eat while migrating ,so they rely on stores of fat .
  when bird migrate ,they fly as a group .to minimize the                      energy needed to fly long distances ,a group of birds51.(  )(fly )together in a V-shape .the bird at the front of the "V"uses the most energy because the wind often blows 52.(    )him.every so often ,the birds change positions site that each bird has a turn at the front ,and everyone gets a rest .
  53.Nav(    )is also an important part of the journey .birds find where they are going birds us
ing visual clues ,such as Rivers coastlines,and  mountain ranges.In addition ,they use the sun and the star for guidance .54.(    )(amaze),they also use the earth's invisible  magnetic  force for direction.this gives them a natural sense of north and south ,like a kind of internal compass .
  Many studies indicate that migratory  birds fly along the same course every year .researchers decide to test this using "bird banding ".they first capture a migratory bird and attach a tag to its foot .this tag has an ID number on it ,55.(    )is stored in a database .they then set the bird free and track its movement .bird banding has shown that many birds follow the same route year after year .
Questions 61-65 are based on the following passage. 
    One of the hardest things for any sportsperson to do is to know when to retire .do you retire when you are at your physical peak or do you wait until your body (or your coach )tells you that it's time to go ?but even harder is finding the answer to the question "what am i going to do with the rest of my life ?"
    61(          )"there 's a high risk of depression and people often find adjusting to a new way of life difficult ",says Ian Cockerill ,a sports psychologist ."for sport people ,There's an extra trauma -the loss of the glamour .that 's the hardest part ."as Eddie Araro ,the us jockey says ,"when a jockey retires ,he becomes just another little man ."
  62(      )perhaps they just can 't stand life without the "high "of playing professional sport .Michael Jordan ,the greatest basketball player of all time ,retired three timeshare .he retired once from the Chicago bulls,made a successful comeback with the bulls,then retired again .his second comeback with an inferior team ended in failure and he retired for ever at the age of 38.Jordan said ,"there will never be anything in do that will fulfill me as much as competing did ."
  63(            )Muhammad Alice needed the money ,but his comeback fight ,at the age of 39，against Trevor Berbick ,was one of the saddest spectacles in modern sport .after losing to Berbick ,Alice retired permanently .three years later he developed Parkinson 's disease .
  64(          )as Jimmy greaves ,an ex-England international footballer said ,"I think that a lot of players would prefer to be shot once their career is over ."many of them spend their retirement in a continual battle against depression,alcohol ,or drugs.
  65(          )Franz Beckenbauer is a classic example of a footballer WHO won everything with his club ,Bayern Munich .after retiring he became a successful coach with Bayern and finally president of the club .John McEnroe ,the infamous "bad boy "of tennis ,is now a highly respected and highly paid TV commentator .another good example is world famous Chinese table tennis player -Deng Yaping.after retiring at the end of the 1997season ,Deng served on the international Olympic committee's ethics and athletes commissions.she is also a member of the elite Laureus World Sportswear academy ,and a member of the Chinese people 's political consultative conference .Deng Yaping becomes deputy secretary of China communist youth league Beijing committee later .but sadly ,for most sportspeople these cases are the exceptions .\
  A.for some people the pain of saying goodbye never leaves them .
glamour
  B.others can 't resist the chance of one last "pay day ".
  C.however ,some famous sports persons are much easier to develop some typical psychological disease .
  D.but for the lucky few ,retirement can mean a successful new career .
  E.when you hear the final whistle you have to leave as soon as possible .
  F.retirement for people in general is traumatic .
  G.some sportspeople go on playing too long .
  Would you believe that your diet can make a big difference in keeping a youthful appearance ?It seems strange to think that the food we take in could result in fewer wrinkles .wouldn't it be better to put things on our skin rather than in our mouths ?
  well ,according to one scientific theory ,our bodies start aging because of oxidation .this means the certain oxygen -containing molecules in our cells ,called free radicals ,have th
e capability to attach to and damage parts of our cells ,including our DNA .our bodies can repair this damage ,but as we get older ,these repair mechanisms start to break down ,resulting in the signs of aging .free radicals are actually reduced by our bodies ,but their numbers can also increase because of the food we eat .

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