题目内容：

 

As skies are filled with millions of migrating（迁徙） birds, European scientists say the seasonal wonder appears to be strange. The fatter the bird, the better it flies.

The results of their study led to a theory opposite to a central one of aerodynamics(空气动力学), which says that the power needed to fly increases with weight.

For birds, obviously, the cost of flying with heavy fat is much smaller than we used to think. Researchers found that red knot wading birds double their normal body weight of 100 grams before making their twice-a-year nonstop flight between the British Isles and the Russian Arctic.Distance;5,000 kilometers.

Another study in the magazine Nature measured the advantage of flying in an aerodynamic group which allows birds to save energy by flying smoothly and quietly in the lead bird’s air stream.

Flying in groups, their heart rates were 14.5 percent lower than flying alone, according to Henri, a French scientist. The findings help explain how birds complete difficult migrations. Researchers had thought stronger birds would have the best chance to survive.

The first study suggests that building up fat to be burnt as fuel during the migration is worth more than the energy it take to carry the additional weight.

In the study, researchers said their team studied the birds flown at different body weights during 28 simulated(模拟的)flights. They forced a small amount of special water into the birds’ bodies so that they could measure the amount of energy burnt during the flight.

1.A red knot wading bird of 100 grams will probably weigh ________before making its nonstop migrating flight.

  A.50 grams           B.100 grams        C.150 grams       D.200 grams

2.During their migrating flight, red knot wading birds can save energy by flying________.

   A. separately         B. alone             C. in groups        D. in pairs

3.A ________red knot wading bird has a better chance to survive during its migrating flight.

  A. stronger            B. weaker            C. thinner         D. fatter

4.The best title for this passage may probably be ________ .

  A. Birds Thin Down For Journey                 B. Birds Fatten Up For Journey

  C. How Birds Build Up Fat For Journey           D. How Birds Burn Energy For Journey