¡¡¡¡reduced evaporation.
¡¡¡¡Another problematic method is to reconstruct former
¡¡¡¡climates on the basis of pollen profiles. The type of vege-
¡¡¡¡tation in a specific region is determined by identifying
¡¡¡¡£¨45£© and counting the various pollen grains found there.
¡¡¡¡Although the relationship between vegetation and
¡¡¡¡climate is not as direct as the relationship between
¡¡¡¡climate and lake levels£¬ the method often works well in
¡¡¡¡the temperate zones. In arid and semiarid regions in
¡¡¡¡£¨50£© which there is not much vegetation£¬ however£¬ small
¡¡¡¡changes in one or a few plant types can change the
¡¡¡¡picture dramatically£¬ making accurate correlations
¡¡¡¡between neighboring areas difficult to obtain.
¡¡¡¡1. Which of the following statements about the difference between marine and continental sedimentation is supported by information in the passage£¿
¡¡¡¡£¨A£© Data provided by dating marine sedimentation is more consistent with researchers' findings in other disciplines than is data provided by dating continental sedimentation.
¡¡¡¡£¨B£© It is easier to estimate the age of a layer in a sequence of continental sedimentation than it is to estimate the age of a layer in a sequence of marine sedimentation.
¡¡¡¡£¨C£© Marine sedimentation is much less widespread than continental sedimentation.
¡¡¡¡£¨D£© Researchers are more often forced to rely on extrapolation when dating a layer of marine sedimentation than when dating a layer of continental sedimentation.
¡¡¡¡£¨E£© Marine sedimentation is much more continuous than is continental sedimentation.
¡¡¡¡2. Which of the following statements best describes the organization of the passage as a whole£¿
¡¡¡¡£¨A£© The author describes a method for determining past climatic conditions and then offers specific examples of situations in which it has been used.
¡¡¡¡£¨B£© The author discusses the method of dating marine and continental sequences and then explains how dating is more difficult with lake levels than with pollen profiles.
¡¡¡¡£¨C£© The author describes the common requirements of methods for determining past climatic conditions and then discusses examples of such methods.
¡¡¡¡£¨D£© The author describes various ways of choosing a material for determining past climatic conditions and then discusses how two such methods have yielded contradictory data.
¡¡¡¡£¨E£© The author describes how methods for determining past climatic conditions were first developed and then describes two of the earliest known methods.
¡¡
