6、As skies are filled with millions of migrating(遷徙)birds, Eutopean scientists say the seasonal weadcr appears to be strange; the fatter that bird, the better it flies.
    The results of their study led to a theory opposite to a eentral one of acrodynamies(空氣動(dòng)力學(xué)), whieh says that the  power needed to fly inereases with weight.
    For birds, obvionsly, the cost of flying with heavy fat is much smalleg than we used to think. Resenrchers found that red knoll wading birds double their normal body weight of 100 grams before making their twice-a-year nonstop flight between the Brilish lsles and the Russian Arctic. Distance; 5, 000 kilometers.
    Another study in the magazine Naturn measured the ndvanrage of flying in an acrodynamic group which allows birds to save energy by flying smoothly and quielly in the lead bird’s air strearn.

 Flying in groups, their heart rates were 14.5 pereenl lower than flying alone, according to Henri, a French scientist. The findings help explain how birds complets difficult migrations. Rescarehers had thought that thinner, 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 takes to carry the additional weight.
    In the study, researeherd said their learn studied the birds flown at different body weights during 28 simulated(模擬的)flights. They foreed 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 migraling flingt.

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 not wading hird has a benet 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