Question

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.”

　 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.

　 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.”

68. The first humans into the New World brought dogs along with them because dogs　　　　 .

　 A. kept people company B. were easy to stay alive

C. helped protect the supplies D. offered excellent service

69. The underlined word “remains” in Paragraph 3 probably refers to 　　　　　.

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

70. According to the study described in Paragraph 3, 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 studied were not from dogs brought by Europeans

D. the bones found by the gold miners were from American wolves

71. The passage mainly talks about 　　　　　.

　 A. the DNA study of dogs in NorthAmerica 　

B. the origin of the North American dogs

C. why ancient people brought dogs to America 　

D. the difference between Asian and American dogs

Answer 1

DACB