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GRE阅读模拟在线练习附答案一百八十八

2019-01-20 15:24:00来源：网络

　　对于GRE阅读部分，最好的练习资料就是模拟资料。通过模拟练习，可以让大家更好地发现自己在备考中的不足，重点攻克自己的短板内容，有效的提升阅读分数。下面新东方在线GRE频道为大家整理了详细的内容，供大家参考。

　　点击查看》》》【GRE阅读真题在线练习附答案汇总】

　　The primary method previously used by paleontologists to estimate climatic changes that occurred during Pleistocene glacial cycles was the determination of 18/O16/O ratios in calcareous fossils. However, because this ratio is influenced by a number of factors, the absolute magnitude of the temperature difference between Pleistocene glacial and interglacial cycles could not be unequivocally ascertained. For example, both temperature fluctuations and isotopic changes in seawater affect the 18O/16O ratio. And. since both factors influence the ratio in the same direction, the contribution of each to the 18O/16O ratio cannot be determined.

　　Fortunately, recent studies indicate that the racemization reaction of amino acids can be used to determine more accurately temperatures that occurred during Pleistocene glacial cycles. Only L-amino acids are usually found in the proteins of living organisms, but over long periods of geological time these acids undergo racemization, producing D-amino acids, which are not found in proteins. This reaction depends on both time and temperature thus, if one variable is known, the reaction can be used to calculate the other.

　　It can be inferred from the passage that determination of the temperatures mentioned in line 18 through 18O/16O ratios and determination through racemization reactions both require which of the following?

　　A.Calcium deposits known to be from Pleistocene seas

　　B.Proteins containing both L-amino acids and D-amino acids

　　C.Glacial debris from both before and after the Pleistocene period

　　D.Fossil material from organisms living during the Pleistocene period

　　E.Proteins containing both amino acids and 18O

　　The passage suggests that the 18O/16O ratio could be used more successfully as a means of measurement if scientists were able to?

　　A.determine the 18O/ 16O ratio in living animals as well as in fossil remains

　　B.locate a greater number of calcareous fossils from the Pleistocene glacial and interglacial cycles

　　C.locate the factors other than temperature fluctuations and isotopic changes in seawater that affect the 18O/16O ratio

　　D.arrive at more exact determinations of which amino acids are found in the proteins of living organisms

　　E.isolate the relative effects of temperature fluctuations and isotopic changes in seawater on 18O/16O ratios

　　The information in the passage can be used to answer which of the following questions?

　　Ⅰ Do temperature variations and isotopic changes in seawater cause the 18O/16O ratio to shift in the same direction?

　　Ⅱ What are the methods used to determine the18 O/16O ratio?

　　Ⅲ Is the study of raceminzation reactions useful in estimating climatic changes that occurred during Pleistocene glacial cycles if only one of the two important variables is known?

　　A.Ⅰonly

　　B.Ⅰand Ⅱ only

　　C.Ⅰand Ⅲ only

　　D.Ⅱand Ⅲ only

　　E.Ⅰ,Ⅱ,and Ⅲ

　　According to the passage, before the recent experiments described in the passage were completed, scientists could

　　A.determine temperatures only for Pleistocene seas

　　B.determine temperatures that occurred during Pleistocene glacial cycles only by examining fossil remains

　　C.measure changes in temperatures that occurred during Pleistocene glacial cycles with only questionable accuracy

　　D.only partially identify factors tending to lower Pleistocene temperatures

　　E.accurately determine temperatures only for land masses affected by glaciating

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