GRE阅读练习每日一篇(三十)_GRE阅读

GRE阅读练习每日一篇(三十)

　　Lack of a method for identifying mycorrhizal fungi

　　Difficulties surrounding laboratory production of specimens for study

　　Difficulties ensuing from the high cost and scarcity of superphosphate fertilizers

　　20. The passage suggests which of the following about the increased resistance to harmful root fungi that some plants infected with mycorrhizal fungi seem to exhibit?

　　There are at least three hypotheses that might account for the increase.

　　An explanation lies in the fact that mycorrhizal fungi increase more rapidly in number than harmful root fungi do.

　　The plants that show increased resistance also exhibit improved nitrogen fixation.

　　Such increases may be independent of mycorrhizal infection.

　　It is unlikely that a satisfactory explanation can be found to account for the increase.

　　In the early 1950 s, historians who studied preindustrial Europe began, for the first time in large numbers, to investigate more of the preindustrial European population than the 2 or 3 percent who comprised the political and social elite: the kings, generals, judges, nobles, bishops, and local magnates who had hitherto usually filled history books. One difficulty, however, was that few of the remaining 97 percent recorded their thoughts or had them chronicled by contemporaries. Faced with this situation, many historians based their investigations on the only records that seemed to exist: birth, marriage, and death records. As a result, much of the early work on the nonelite was aridly statistical in nature; reducing the vast majority of the population to a set of numbers was hardly more enlightening than ignoring them altogether. Historians still did not know what these people thought or felt.