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Which of the following can be inferred from the passage about plant cultivation in the Yangtze Basin?
Wildcats are improbable candidates for domestication. Like all felids [cats], wildcats are obligate carnivores, meaning they have a limited metabolic ability to digest anything except proteins. Wildcats live a solitary existence and defend exclusive territories, making them more attached to places than to people. Furthermore, cats do not perform directed tasks and their actual utility is debatable; even as mousers, in this latter role, terrier dogs and ferrets are preferable. Accordingly, there is little reason to believe an early agricultural community would have sought out and selected the wildcat as a house pet. Rather, the best inference is that wildcats exploiting human environments were simply tolerated by people and, over time and space, they gradually diverged from their "wild" relatives.
The author would most likely agree that in early agricultural communities cats would have been
Which of the following best describes the function of the highlighted sentence in the context of the passage as a whole
George Milner cites three primary problems with the labeling of Cahokia, the large archaeological site by the Mississippi River, as a state rather than a chiefdom. First, finds at Cahokia are essentially similar to finds at other Mississippian chiefdoms, except that the amount of earth moved in building the mounds at Cahokia was greater than elsewhere. Second, fewer people lived at Cahokia than is commonly estimated (Milner estimates that there were only a few thousand inhabitants, more common estimates are 10,000 or 20,000 inhabitants); therefore, extensive taxes, trade, and tribute were not necessary to support them. Finally, while there is evidence of extensive earth movement, craftwork, trade, and elite at Cahokia, this does not indicate that Cahokia was politically centralized, economically specialized, or aggressively expansionistic.
The primary purpose of the passage is to
The passage implies that political centralization is a feature that
Ecologists had assumed that trees in the consistently warm tropics grew at a slow but steady rate, unvarying from year to year. However, a study at La Selva, Costa Rica, showed that trees grew less in hotter years and more in cooler ones: between 1984 and 2000, dramatic differences occurred in the six species of trees studies, with trees adding twice as much wood in some cooler years as they did in the scorching El Nino year of 1997-1998. Because tree growth is an index of the balance between photosynthesis, in which trees absorb carbon dioxide (CO2) from the atmosphere and release oxygen, and respiration, in which the opposite occurs, the La Selva data were the first hint that rapidly rising global temperatures, driven by human-generated emissions of CO2, may be pushing tropical forests to release more CO2, thereby intensifying global warming. This raised serious questions about a popular theory that tropical forests act as a sponge, soaking up much of the excess CO2 that humans pump into the atmosphere. The La Selva data are consistent with a model of global CO2 flux developed by Keeling, who concluded that the amount of CO2 taken up in tropical landmasses rose in cooler years and fell in hotter ones, accounting for year-to-year changes in the amount of CO2 that stays in the atmosphere.
The primary purpose of the passage is to
The passage supports which of the following statements about the trees in the La Selva study?
The passage suggests that as temperatures rise, trees in the tropical regions
In the 2,000-year period immediately before European contact, many native groups of the Northern Plains of North America specialized in big-game hunting, subsisting primarily on bison. Bison routinely became fat-depleted in the spring, reducing their nutritional value, yet these groups did not supplement their diets with the nutritious, fat-rich fish that were abundantly available. Malainey et al. find a possible explanation in late-eighteenth- and early-nineteenth century accounts from three frontiersmen who had adapted to lean-meat diets during extended periods in the plains. Each had an opportunity to consume fish after extended meat dependence and upon eating it, became weak and ill. Malainey notes that prolonged lean meat dependence renders the body incapable of digesting lipids (fats), perhaps explaining native hunters fish avoidance.
The author of the passage mentions accounts from three white frontiersmen primarily in order to
Select the sentence that describes the phenomenon that the passage is concerned with finding an explanation for.
Click on the sentence in the passage that speculates about the effect of human intervention on an observation.
Migratory songbirds breeding in Eurasias temperate forests depend on a summer flush of insects, particularly caterpillars, to feed themselves and their offspring. In some places, these caterpillars are emerging earlier in responses to rising global temperatures. In theory, the songbirds could simply push up their departure from their winter quarters to catch the earlier flush of insect prey. If, however, the birds rely on a fixed cue such as increasing day length to begin flying north, they may be unable to adjust the timing of their migration. Precisely this disruption in the emergence of insects relative to the timing of songbird migration has been identified as the cause of a significant decline in populations of pied flycatchers in the Netherlands.
The primary function of the highlighted sentence is to
According to the passage, populations of insects preyed upon by pied flycatchers.
Widespread climate change challenges traditional notions that preserving specific chunks of land is an adequate way to protect endangered species. Commitment to particular places has taken conservation a long way, but it works only when the climate is relatively stable. When climate change rather than degraded habitat threatens a species` survival in a particular location, moving the species to new locales might become one way of preserving it. Some ecologists argue that such assisted migration is simply a way to mimic the natural process of dispersal: its adherents intend to transport species from places that have become uninhabitable through places that humans have made impassable. Although it has its risks, assisted migration may be a necessary step in the evolution of conservation.
The author of the passage implies that some endangered species are unlikely to migrate naturally to habitats better suited to their survival because

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