2.你观察过下列现象吗？安静的傍晚，狗或猫竖起耳朵警觉地谛听.这是(　　 )

A.狗或猫在谛听无线电波

B.狗或猫在谛听火星发出的声音

C.狗或猫在偷听远处人们手机的对话

D.狗或猫听到人耳所不能觉察的某些频率的声音

1.电影《地道战》中的日军指挥官让人在地下埋几口水缸，并时不时把头探进缸里，以下有几种解释，你认为哪种说法正确？(　　 )

A.甲说：“从水缸中能看见地道里游击队员的像，判断有无游击队员.”

B.乙说：“从水缸中能听见地面下传来的声音，判断有无游击队员挖地道.”

C.丙说：“防止自己的讲话被游击队员偷听.”

D.丁说：“是为了藏匿物品.”

55. The passage suggests that ________.

A. different kinds of birds have different ways to migrate

B. different kinds of birds migrate for various reasons

C. some birds can survive without migrating each season

D. birds’ food sources are becoming rare all over the world

54. Which of the following is true?

A. All birds fly to non-breeding areas each year. 　B. There are 379 species of birds migrating.

C. Two related species have the same behavior.　 D. Computers are used in the research work.

53. The researchers constructed a “supertree” mainly to ________.

A. compare the sizes of different birds

B. make out the relationships between different birds

C. find out what causes birds to leave each season

D. predict when the birds were migratory

52. The scientists used to believe that birds migrate because ________.

A. they want to search for the food they like　　　

B. they can find more food in a different place

C. they can breed their young in a different place

D. the weather turns too cold

51. The passage mainly tells us ________.

A. the real reason for birds’ migration　　 　　　 B. food scarcity that birds face today

C. how birds search for food　　　　　 　　　　　　　 D. when birds migrate

50. We can infer from the passage that in the hotel ______.

A. you can read many newspapers from around the world

B. you can enjoy both the urban and rural exciting lives

C. there are many advanced computers for customers to use

D. there probably are some pictures of snow leopards

C

It’s food scarcity (短缺), not dietary preferences, that motivates birds to migrate thousands of miles back and forth between breeding and non-breeding areas each year, new research shows.

“It’s not whether you eat insects, fruit, nectar or candy bars or where you eat them - it matters how reliable that food source is,” said study leader W. Alice Boyle of the University of Arizona.

To figure out the pressures that drive some birds to leave home for the season, Boyle examined 379 related species of flycatchers and compared their sizes, food types, habitats, migratory behaviors and whether or not they fed in flocks.

To compare the birds, the researchers constructed a “supertree” showing the exact evolutionary (演化的) relationships among different species.

A computer analysis then determined whether a particular species was migratory because it ran in the “family” or whether something in the bird’s environment was forcing it to leave each season.

Boyle and her colleagues found that food scarcity was the number one issue that predicted a species’ migratory behavior.

An alternative strategy that birds use to deal with food scarcity is to forage (四处搜寻) in flocks, because a group is more likely to find a new source of food than a lone individual.

“If you are faced with food scarcity, you have two options,” Boyle said. “You can either forage with other birds, or you can migrate.”

49. You can do all the following in the hotel EXCEPT ______.

A. read free newspapers　　　　　 　　　　　　　 B. surf on the Internet

C. do exercise deep in the night　　 　　　　　　　 D. watch movies as you like

48. The underlined word “complimentary” in the second part means “______”.

A. available　 　　　　 B. expensive　　 　　　　　 C. free　　 　 　　　　　　　 D. entertaining