When people first walked across the Bering Land Bridge thousands of years ago, d

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When people first walked across the Bering Land Bridge thousands of years ago, dogs were by their sides, according to a study published in the journal Science.
Robert Wayne of the University of California, Los Angeles, and Jennifer Leonard of the Smithsonian Institute, used DNA material—some of it unearthed by miners in Alaska—to conclude that today’s domestic dog originated in Asia and accompanied the first humans to the New World about 10,000 to 15,000 years ago. Wayne suggests that man’s best friend may have enabled the tough journey from Asia into North America. “Dogs may have been the reason people made it across the land bridge,” said Wayne. “They can pull things, carry things, defend you from fierce animals, and they’re useful to eat.”
Researchers have agreed that today’s dog is the result of the domestication(驯化) of wolves thousands of years ago. Before this recent study, a common thought about the precise origin of North America’s domestic dog was that Natives domesticated local wolves, the descendents(后代) of which now live with people in Alaska, Canada, and the Lower 48.
Dog remains from a Fairbanks-area gold mine helped the scientists reach their conclusion. Leonard, an evolutionary biologist, collected DNA from 11 bones of ancient dogs that were locked in permafrost(永冻层) until Fairbanks miners uncovered them in the 1920s. The miners donated the preserved bones to the American Museum of Natural History in New York City, where they remained untouched for more than 70 years. After borrowing the bones from the museum, Leonard and her colleagues used radiocarbon techniques to find the age of the Alaska dogs. They found the dogs all lived between the years of 1450 and 1675 A.D., before Vitus Bering and Aleksey Chirikov who were the first known Europeans to view Alaska in 1741. The bones of dogs that wandered the Fairbanks area centuries ago should therefore be the remains of “pure native American dogs,” Leonard said. The DNA of the Fairbanks dogs would also expose whether they were the descendents of wolves from North America.
Along with the Fairbanks samples, the researchers collected DNA from bones of 37 dog specimens(标本) from Mexico, Peru, and Bolivia that existed before the arrival of Columbus. In the case of both the Alaska dogs and the dogs from Latin America, the researchers found that they shared the most genetic material with gray wolves of Europe and Asia. This supports the idea of domestic dogs entering the New World with the first human explorers who wandered east over the land bridge.
Leonard and Wayne’s study suggests that dogs joined the first humans that made the adventure across the Bering Land Bridge to slowly populate the Americas. Wayne thinks the dogs that made the trip must have provided some excellent service to their human companions or they would not have been brought along. “Dogs must have been useful because they were expensive to keep,” Wayne said. “They didn’t feed on mice; they fed on meat, which was a very guarded resource.”
小题1: The underlined word “remains” is closed in meaning to ______.

A．leftover food	B．animal waste
C．dead bodies	D．living environment

小题2:According to the study described in Paragraph 4, we can learn that ______.

A．ancient dogs entered North America between 1450 and 1675 AD

B．the 11 bones of ancient dogs are not from native American dogs

C．the bones discovered by the gold miners were from North American wolves

D．the bones studied were not from dogs brought into North America by Europeans

小题3:What can we know from the passage?

A．Native Americans domesticated local wolves into dogs.

B．Scientists discovered some ancient dog remains in 1920s.

C．Latin America’s dogs are different from North America’s in genes.

D．Ancient dogs entered North America across the Bering Land Bridge.

小题4:The first humans into the New World brought dogs along with them because ______.

A．dogs fed on mice	B．dogs were easy to keep
C．dogs helped protect their resources	D．dogs could provide excellent service

小题5:What does the passage mainly talk about ______.

A．the origin of the North American dogs

B．the DNA study of ancient dogs in America

C．the reasons why early people entered America

D．the difference between Asian and American dogs

答案

小题1:C
小题2:D
小题3:D
小题4:D
小题5:A

解析

试题分析：本文是科普性文章。说明了在几千年前狗陪同人们一起跨过白令大陆桥进入北美大陆，并且在此繁殖起来。而通过检测发掘出的狗骨头的DNA也证实了这一点。
小题1:C 词意猜测题。根据第四段第二句话“Leonard, an evolutionary biologist, collected DNA from 11 bones of ancient dogs that were locked in permafrost(永冻层)”说明是在冰冻层发现的狗的骨头，所以remain应该是尸体。C选项正确。
小题2:D细节题。根据“They found the dogs all lived between the years of 1450 and 1675 A.D before Vitus Bering and Aleksey Chirikov who were the first known Europeans to view Alaska in 1741..”判断可知被研究的骨头不是欧洲人带到北美来的狗的骨头。所以D项正确。
小题3:D细节题。根据第一段“When people first walked across the Bering Land Bridge thousands of years ago, dogs were by their sides, according to a study published in the journal Science.”所以D选项正确。
小题4:D 细节题。根据第二段“Wayne suggests that man’s best friend may have enabled the tough journey from Asia into North America. “Dogs may have been the reason people made it across the land bridge,” said Wayne. “They can pull things, carry things, defend you from fierce animals, and they’re useful to eat.”这些都说明了人们之所以带着狗，是因为它们能为人们提供服务，由用处。所以D正确。
小题5:A推理题。文章第一段提到狗和人们一同跨过the Bering Land Bridge，第二三四五段研究狗的DNA“ to conclude that today’s domestic dog originated in Asia”，“Researchers have agreed that today’s dog is the result of the domestication(驯化) of wolves thousands of years ago”所以文章中心是谈论狗的起源。