問題詳情

【Reading Comprehension】Radiocarbon dating and tree-dating, in combination, have provided a very powerful tool to establish atime spectrum for more recent dates in the past. The initial idea for dating by tree rings can be traced backto 1811. Modern scientific tree-ring dating, dendrochronology, stems from pioneering work in early 1900s.Usually, but not always, trees produce one ring each year. This ring is formed by the cambium, whichlies between the old wood and the bark. In spring, wood cells with large lumens are manufactured, but insummer and autumn, the cells become smaller and more thick-walled until the onset of winter, in which theproduction of a new cell stops. The same process is repeated in the following year. In this way a year’sgrowth (annual ring) is imprinted as new wood. The demarcation line between summer and autumn wood ofthe previous year, with its characteristic small cells, and the spring wood of the year following, with its largecells, enables annual rings to be counted relatively easily.Growth rings, however, are not always the same thickness. They vary for several reasons.Environmental factors rigidly control the degree of growth of an annual ring or determine whether, in fact, anannual ring appears or not in any particular year. Thus in a specific locale or, more accurately, a specificclimatic province, tree-ring counts will reflect climatic conditions and variations due to inequalities of climatefrom year to year. In years with abnormal drought, for example, narrow rings are produced and sometimesno ring at all. In this way a fossil record is imprinted for as long as the wood remains intact. From thispattern a historical template can be constructed to correlate one set of growth rings in one tree with a set ofgrowth rings in another tree or piece of timber.Another important factor is that tree-ring growth varies with age of the tree. As the tree matures, therings become narrower, and this results in the central rings being wider than those on the outer part of thetree.
31.What does the passage mainly discuss?
(A) The effect of drought on tree-ring growth.
(B) The history of dating trees.
(C) The problems of tree-ring dating.
(D) The formation of growth rings in trees.

參考答案

答案：D
難度：適中0.626866
統計：A(4),B(17),C(4),D(42),E(0)

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