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Researchers suspect that meteorites (particles of matter that fall to Earth' s surface from space) are pieces of asteroids, the many minor planets primarily inhabiting the region between Mars and Jupiter called the asteroid belt. The most common meteorites are ordinary chondrites-rocks containing tiny flecks of metal. By analyzing the spectrums of sunlight reflected by asteroids to determine the asteroids' chemical composition, researchers have found that most of the brighter asteroids contain the same silicates and other compounds that dominate chondrites. These silicaceous, or S-type, asteroids are the most abundant type in the inner asteroid belt, the part of the asteroid belt from which objects are most likely to escape and travel to Earth. However, S-type asteroids reflect red and infrared light much better than they reflect green, blue, and violet light, suggesting that they have a higher metal content than do ordinary chondrites. This has led at least one researcher to posit that meteorites come from other types of asteroids that are too small and too dim to be detected. However, S-type asteroids could be ordinary chondrites that have been weathered by the effects of the space environment, making them seem redder and more metallic than they really are.
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The primary purpose of the passage is to
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The author of the passage most likely mentions that the inner asteroid belt is "the part of the asteroid belt from which objects are most likely to escape and travel to Earth" in order to
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It can be inferred from the passage that one reason for considering S-type asteroids to be likely sources of meteorites is that S-type asteroids
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Ecologists tend to focus on pristine environments and ignore urban areas. Human beings, and especially their cities, fail to fit neatly into ecological theory-they are seen as an exogenous, perturbing force in nature. Yet people are a global force capable of affecting every ecosystem on the planet. In cities, people mobilize some nutrients and deplete others, create habitats that never before existed, increase temperatures, and, by intent or by accident, manipulate the communities of other species found within city boundaries and beyond. If there is a laboratory where ecological change can be viewed at close hand, it is the city. The processes and dynamics within cities, however, largely elude understanding based on traditional ecological theories.
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It can be inferred from the passage that which of the following statements about traditional ecological theories is true?(Consider each of the choices separately and select all that apply.)
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According to the passage, human beings do not fit neatly into ecological theory for which of the following reasons?
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For Year X, in how many of the six regions did grasses produce pollen for a period of less than three months?
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For approximately what fraction of Year X was pollen produced by both grasses and weeds in the Southwest?
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For Year X, which of the following is closest to the total length, in months, of the time period during which no pollen was produced by trees or grasses in any of the six regions?
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Robert Bakker suggested that plant-eating dinosaurs "invented" flowering plants. He concluded that while Late Jurassic browsers fed on foliage in the canopy and subcanopy layers, the later Cretaceous dinosaurs were predominately grazers that indiscriminately clipped flora to near-ground levels. And because angiosperms (flowering plants) grow and reproduce quickly, early angiosperms would have recovered from this clear-cutting faster than non-flowering gymnosperms, giving them a competitive advantage that eventually led to their dominance. Some argue, however, that most Cretaceous dinosaurs probably did not graze vegetation to the ground and that both angiosperm and gymnosperm seedlings would have survived. They also object to Bakker' s comparison of widespread dinosaur herbivory to mammalian grazing on grasslands, given the absence of evidence that such habitats occurred during the Cretaceous.
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It can be inferred that Bakker would be most likely to agree with which of the following claims about angiosperms?
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The author mentions "canopy and subcanopy layers" primarily in order to
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Because coal contains toxic materials such as arsenic and lead, and its use contributes to air pollution and acid rain, one might therefore conclude that no good case could be made for burning it for fuel. But that depends on where one is starting from. Switching to coal from firewood is beneficial for both the environment and the health of the individual. Firewood use results in deforestation, loss of ecosystems, and degradation of soil quality. Wood fires are also sooty, and their particulates contribute to global warming by decreasing the reflectivity of snowfields. Finally, firewood is generally burned in homes with poor ventilation and poses a greater health risk to the individuals than they would experience from a coal-fired utility that provides electricity to their homes.
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The passage indicates which of the following about firewood? (Consider each of the choices separately and select all that apply.)
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The author mentions arsenic and lead primarily in order to
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For how many of the five vehicle types is the number of silver vehicles less than 20 percent of the total number of vehicles of that type?
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By approximately what percent does the total number of green vehicles exceed the total number of brown vehicles?
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