【正文】 ess than two million years, small populations of stray animals and plants from the South American mainland that managed to colonize the Galapagos Islands gave rise to all the species that now inhabit the islands.When oceanic islands are far enough apart to permit populations to evolve in isolation, but close enough to allow occasional dispersions to occur, they are effectively outdoor laboratories of Galapagos island chain is one of the world s greatest showcases of evolution Each island was born from underwater volcanoes and was gradually covered by organisms derived from strays that rode the ocean currents and winds from other islands and continents. Organisms can also be carried to islands by other organisms, such as sea birds that travel long distances with seeds clinging to their feathers.The species on the Galapagos Islands today, most of which occur nowhere else, descended from organisms that floated, flew, or were blown over the sea from the South American mainland For instance, the Galapagos island chain has a total of thirteen species of closely related birds called Galapagos finches These birds have many similarities but differ in their feeding habits andtheir beak type, which is correlated with what they eat Accumulated evidence indicates that all thirteen finch species evolved from a single small population of ancestral birds that colonized one of the isolated on the island after migrating from the mainland, the founder population may have undergone significant changes in its gene pool and bee a new species. Later, a few individuals of this new species may have been blown by storms to a neighboring island. Isolated on this second island, the second founder population could have evolved into a second new species, which could later recolonize the island from which its founding population each Galapagos island has multiple species of finches, with as many as ten on some islands.paragraph 1Biologist Ernst Mayr defined a species as “an actually or potentially interbreeding population that does not interbreed with other such populations when there is opportunity to do so.” A key event in the origin of many species is the separation of a population with its gene pool (all of the genes in a population at any one time) from other populations of the same species, thereby preventing population interbreeding With its gene pool isolated, a separate population can follow its own evolutionary course. In the formation of many species, the initial isolation of a population seems to have been a geographic barrier This mode of evolving new species is called allopatric speciation. word “key” in the passage is closest in meaning to word “initial” in the passage is closest in meaning to to paragraph 1. allopatric speciation is possible whenA. a population contains all the different genes present in a species at a particular timeB. a population bees isolated due to the presence of a geographic barrierC. genetic mixing begins to occur in previously separate populations of a speciesD. a species is successful in crossing a geographic barrierparagraph 1amp。 antelope squirrel has a more limited range in deserts south of the Grand Canyon. paragraph 3, the author contrasts a variety of organisms to illustrate which of the following points?A. Geographic barriers are less likely to keep apart populations of plants than populations of animals.B. Geographic barriers are more likely to keep apart populations of large organisms than populations of small organismsC. Some members of a species are able to cross geographic barriers, while other members of the same species are not.D. The effectiveness of geographic barriers in keeping organisms apart depends on an organism’s ability to move across barriers. 3 supports the idea that whitetailed antelope squirrels and Hams39。s greatest showcases of evolution” primarily because ofA. the richness of the volcanic soil of each of the islands in the chainB. the distance of the individual islands from each other and from the mainlandC. the relativity long time it took for the islands to bee covered by organismsD. the outdoor laboratories that scientists have built on the islands to study evolutionparagraph 6The species on the Galapagos Islands today, most of which occur nowhere else, descended from organisms that floated, flew, or were blown over the sea from the South American mainland For instance, the Galapagos island chain has a total of thirteen species of closely related birds called Galapagos finches These birds have many similarities but differ in their feeding habits and their beak type, which is correlated with what they eat Accumulated evidence indicates that all thirteen finch species evolved from a single small population of ancestral birds that colonized one of the islands. Completely isolated on the island after migrating from the mainland, the founder population may have undergone significant changes in its gene pool and bee a new species. Later, a few individuals of this new species may have been blown by storms to a neighboring island. Isolated on this second island, the second founder population could have evolved into a second new species, which could later recolonize the island from which its founding population emigrated. Today each Galapagos island has multiple species of finches, with as many as ten on some islands. to paragraph 6. what is true about the thirteen species of Galapagos finches?A. All thirteen species are now found on most of the Galapagos IslandsB. All thirteen species are descended from the same population of ancestral birdsC. All thirteen species evolved on the island that was originally colonized by finches from the mainland.D. All thirteen species occur only in small, pletely isolated populations. at the four squares [■] that indicate where the following sentence could be added to the passage.This process of speciation and colonization could have been repe