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An annual census of wolves at Yellowsto ne National Park has found a sharp drop in the population. But park biologists, who suspect a deadly disease, canine parvovirus, say they will let nature take its course. "Parvo can be vaccinated for and can be treated, but we wouldn't do it because we couldn't catch every animal," Daniel Stahler. a park waif biologist, said. "And this allows them to build up a natural resistance."
The census found 22 pups, compared with 69 last year. The total count of wolves dropped m 118 from 171, the lowest since 2000. "It was somewhat devastating to have such poor pup survival," Mr. Stahler said. "But research shows that young pups can bounce back from it quite successfully." That pups have suffered the decline seems to suggest the culprit is parvo, said Ed Bangs, waif recovery coordinator for the United States Fish and Wildlife Service here. Nursing pups receive immunity from their mother's milk. but the immunity drops when nursing stops.
The large number of wolves in the park might also be a factor. "When you have a big litter and adults are having trouble killing enough to feed all these pups, and the animals are stressed, parvo flares up," Mr. Bangs said. "If you have 15 brothers and sisters instead of 3, you don't get enough to eat; parvo kills you."
Canine parvovirus was discovered in the United States in 1978. Extremely hardy, the disease spread rapidly to domestic dogs and then into wild animal populations. Biologists suspect that it was introduced to Yellowstone by a tourist's infected dog or a coyote. Because parvo is so hardy, it persists in the soil for months. A wolf could catch it from simply sniffing infectious soil. the biologists said. The disease has hit wolves on the northern range, the elk-filled meadows of the northern half of the park, especially hard. Out of 49 pups born there, 8 survived.
Some scientists, including Mr. Bangs, theorize that the park may have overshot its capacity for wolves and that the numbers are naturally adjusting downward, with disease being one of the agents. The long-term carrying capacity of the park, he said, is probably 110 to 150 wolves.
Wolves have been killed in other ways, too. Frequent encounters among competing wolf packs are the biggest cause of death among adults. In the first five years of their reintroduction to the park, one or two animals a year were killed by other wolves. That number has risen to four or five a year.
Vehicles also take a toll, Fourteen wolves have been killed by vehicles in the last 10 years, eight of them near Mile Marker 30 on Route 191, a straight stretch on the western side of the park where motorists tend to speed and wolves are plentiful.

单选题 By saying "let nature take its course", the biologists mean______.

【正确答案】 D

【答案解析】推理判断题。原句是“But park biologists, who suspect a deadly disease, canine parvovirus, say they will let nature take its course.”根据下文，治疗这种疾病有疫苗，但是公园不会给狼注射，这样做一是因为不可能抓住每只狼，二是这样有利十狼建立起自然抵抗力。“let nature take its course”字面意义是“让自然按其常规运行”，根据前后文，这里就是说不采取任何措施，让自然来决定狼的生存。因此，D是正确答案。

单选题 37 According to the third paragraph, Mr. Bangs holds the view that______.

单选题 Canine parvovirus is a disease which______.

【正确答案】 C

【答案解析】事实细节题。这个题目是关于犬类疾病的，选项A“幼犬对该疾病有免疫力”，根据第二段"That pups have suffered the decline seems to suggest the culprit is parvo, said Ed Bangs，“Nursing pups receive immunity from their mother's milk, but the immunity drops when nursing stops.”可知，正是由于幼犬没有免疫力才感染这种疾病，造成数量下降的；B“只在家养犬中传播”，根据第四段“the disease spread rapidly to domestic dogs and then into wild animal populations”(除了在家犬中传播外，这种疾病还会蔓延到野生动物中去)可判断这与文章内容不符；C“这种疾病非常顽强，可以在土壤中存活几个月”，根据第四段"Because parvo it so hardy, “persists in the soil for months.”一句可知这是正确论述；D“只对北方区域的犬造成影响”，而第四段说的是“The disease has hit wolves on the northern range… especially hard.”指这种疾病在北方区域的犬中尤为厉害，而并不是只会影响北方区域的犬。