简述中华鱼蚤病的流行情况。

《汽车贷款管理办法》规定，汽车贷款的贷款期限(含展期)不得超过( )年。

A．1

B．2

C．3

D．5

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

特种兵过山谷的一种方法可简化为图示情景。将一根长为2d的不可伸长的细绳两端固定在相距为d的A、B两等高点，绳上挂一小滑轮P，战士们相互配合，沿着绳子滑到对面。如图所示，战士甲（图中未画出）水平拉住滑轮，质量为m的战士乙吊在滑轮上，脚离地，处于静止状态，此时AP竖直，然后战士甲将滑轮从静止状态释放，若不计滑轮摩擦及空气阻力，也不计绳与滑轮的质量，求：

（1）战士甲释放前对滑轮的水平拉力F；

（2）战士乙滑动过程中的最大速度。

急性重症胰腺炎并发感染或胆道感染时，最主要的表现为（）

A.寒战高热

B.寒战并不发热

C.呕吐加重

D.腹痛加重

E.腹痛减轻