Dendrochronology, the study of tree-ring records to glean information about the past, is possible because each year a tree adds a new layer of wood between the existing wood and the bark. In temperate and subpolar climates, cells added at the growing season's start are large and thin-walled, but later the new cells that develop are smaller and thick-walled; the growing season is followed by a period of dormancy. When a tree trunk is viewed in cross section, a boundary line is normally visible between the small-celled wood added at the end of the growing season in the previous year and the large-celled spring wood of the following year's growing season. The annual growth pattern appears as a series of larger and larger rings. In wet years rings are broad; during drought years they are narrow, since the trees grow less. Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.

However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate. And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count. Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.

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The passage is primarily concerned with


evaluating the effect of climate on the growth of trees of different species

questioning the validity of a method used to study tree-ring records

explaining how climatic conditions can be deduced from tree-ring patterns

outlining the relation between tree size and cell structure within the tree

tracing the development of a scientific method of analyzing tree-ring patterns

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题目分析：

题目释义：

主旨题目

考点：

主旨（Main idea）
旨在考察我们对文章整体的把握程度，对文章的结构的分析能力和把控能力，以及对作者逻辑的判断。

这篇文章的第一段讲了年轮的形成，和气候的关系，说明了判断方法。第二段讲了一些“exception”，但总体还是在为上段服务。



选项分析：

A选项：评估气候对不同种类的树木生长的影响。文中提及的是气候对年轮生长的影响，没有提到过对树木生长的影响。

B选项：质疑一个研究树木年轮的方法。这个选项有一定的迷惑性，文中的第二段确实提出了这种方法的一些潜在问题，但是作者没有质疑“D”这个方法的意思。

C选项：Correct. 解释气候条件怎样被反应在树木的年轮中。第一段在文中介绍了原理，第二段提出让步，这两者结合有效的解释了气候条件在年轮中的反应。

D选项：概要树木的大小和细胞的结构的关系。文中没有提到树木的大小与细胞结构的关系。这个选项属于无中生有。

E选项：探查一个科学的分析年轮的模式的方法的发展过程。文中没有提及探究“D”的发展过程，只是介绍了原理和让步出潜在的问题。

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Prep2007E1-RC