But now, a team of scientists created a temperature record for that area dating back 12,000 years. It is the first such record for a region in the central part of North America stretching from southern Canada to north Texas. Temperature records are usually created by assessing fossil pollens ( 花粉 ), which are better preserved in damp areas. But in the Great Plains, pollen saving is virtually nonexistent. Nordt developed the first comprehensive temperature record by assessing the behavior of the stable composition of buried soils. He examined the relationship between the waves in the abundance of warm-season grasses and the mean July temperature from 61 modern native grasslands and applied a mathematical equation of what he found in the modern record to the buried soil 51. According to the passage, the North Amorican Great Plains refers to the region in the central part of North America ____.

Temperature Record

While temperature records in history exist for certain regions of the United States, like the East Coast and the Northwest, no such record exists for the North American Great Plains. But now, a team of scientists created a temperature record for that area dating back 12,000 years. It is the first such record for a region in the central part of North America stretching from southern Canada to north Texas. 

Temperature records are usually created by assessing fossil pollens ( 花粉 ), which are better preserved in damp areas. But in the Great Plains, pollen saving is virtually nonexistent. Nordt developed the first comprehensive temperature record by assessing the behavior of the stable composition of buried soils. He examined the relationship between the waves in the abundance of warm-season grasses and the mean July temperature from 61 modern native grasslands and applied a mathematical equation of what he found in the modern record to the buried soil 

51. According to the passage, the North Amorican Great Plains refers to the region in the central part of North America ____.

A. ranging from northem Texas to north Canada

B. ranging from southern Canada to north Texas

C. ranging from northern Canada to south Texas

D. ranging from southern Texas to south Canada

52. Nordt developed the first comprehensive temperature record for the Great Plains by ___.

A. testing the mean July temperature fom 61 modern nat ve grasslanids

B. assessing the behnr o the stable compositon of buried solls

C. examining fuctuntionEin the tbundonce of warm-season grasses