The now extinct passenger pigeon has the dubious honor of being the last species anyone ever expected to disappear. At one point, there were more passenger pigeons than any other species of bird. Rough 26 of their population went as high as five billion and they accounted for around 40 percent of the total indigenous bird population of North America in the early 19th century.
Despite their huge population, passenger pigeons were 27 to human intrusion into their nesting territory. Their nests were shabby things and two weeks after the eggs 28 , the parent pigeons would abandon their offspring, leaving them to take care of themselves. People discovered that these baby pigeons were really tasty, and the adult birds were also quite 29 . First the native Americans and then the transplanted Europeans came to consider the birds a great 30 .
By the 1850s, commercial trapping of passenger pigeons was proceeding at an 31 pace. Hundreds of thousands of the birds were being harvested every day to be made into popular pigeon pies. In addition, large 32 of the pigeons' nesting territory were being cleared away for planting crops and creating pasture land. As numerous as the passenger pigeons were, they were not an 33 resource. By the 1880s, it was noticed that the bird population had become seriously 34 . The last passenger pigeons killed in the wild were shot in 1899.
Eventually those billions and billions of birds shrank to a single remaining 35 , a passenger pigeon named Martha? who died on September 1, 1914, in captivity at the Cincinnati Zoo. In addition to being the end of an era, it was also the first time humans were able to exactly time the extinction of a species.
A) vulnerable I) hatched
B) unprecedented J) expired
C) tracts K) excerpts
D) specimen L) estimates
E) robust M) edible
F) refuge N) depleted
G) plazas O) delicacy
H) infinite
答案解析：
根据语境“Rough ___ of their population went as high as five billion”可知，这里说的是对其种群数量的粗略估计，“estimates”有“估计”之意，所以选L。
根据后文人们捕杀旅鸽以及它们巢穴被破坏后亲鸟抛弃幼鸟等情况可知，旅鸽面对人类侵入其筑巢领地时是很脆弱的，“vulnerable”表示“脆弱的”，所以选A。
根据“the parent pigeons would abandon their offspring”可知，这里说的是蛋孵化两周后亲鸟抛弃幼鸟，“hatched”表示“孵化”，所以选I。
根据“People discovered that these baby pigeons were really tasty”以及并列关系可知，成年鸟也是可食用的，“edible”表示“可食用的”，所以选M。
根据前文人们觉得幼鸟美味，成年鸟也可食用可知，这里说土著居民和欧洲移民都认为这种鸟是一种美味佳肴，“delicacy”表示“美味佳肴”，所以选O。
根据“Hundreds of thousands of the birds were being harvested every day”可知，商业捕杀旅鸽是以前所未有的速度进行着，“unprecedented”表示“前所未有的”，所以选B。
根据“were being cleared away for planting crops and creating pasture land”可知，是大量的旅鸽筑巢区域被清理，“tracts”表示“大片(土地、区域等)”，所以选C。
根据语境可知，尽管旅鸽数量众多，但它们不是一种取之不尽的资源，“infinite”表示“无限的”，这里用否定形式表示“不是无限的”，所以选H。
根据“By the 1880s”以及后文提到最后一只野生旅鸽被射杀可知，到19世纪80年代，人们注意到旅鸽的数量严重减少，“depleted”表示“耗尽的，减少的”，所以选N。
根据“a passenger pigeon named Martha”可知，最后数以亿计的鸟只剩下了一只标本，“specimen”表示“标本”，所以选D。
