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One of the questions of interest in the study of the evolution of spiders is whether the weaving of orb webs evolved only once or several times. About half the 35,000 known kinds of spiders make webs; a third of the web weavers make orb webs. Since most orb weavers belong either to the Araneidae or the Uloboridae families, the origin of the orb web can be determined only by ascertaining whether the families are related.

Recent taxonomic analysis of individuals from both families indicates that the families evolved from different ancestors, thereby contradicting Wiehle‘s theory. This theory postulates that the families must be related, based on the assumption that complex behavior, such as web building, could evolve only once. According to Kullman, web structure is the only characteristic that suggests a relationship between families. The families differ in appearance, structure of body hair, and arrangement of eyes. Only Uloborids lack venom glands. Further identification and study of characteristic features will undoubtedly answer the question of the evolution of the orb web.

The primary purpose of the passage is to

settle the question of whether orb webs evolved once or more than once describe scientific speculation concerning an issue related to the evolution of orb webs analyze the differences between the characteristic features of spiders in the Araneidae and Uloboridae families question the methods used by earlier investigators of the habits of spiders demonstrate that Araneidae spiders are not related to Uloboridae spiders

正确答案： B 耗时：

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当前版本由长颈鹿在哪里呀更新于2019-01-04 11:40:36 感谢由长颈鹿在哪里呀对此题目的解答所做出的贡献。

首先D可以很快排除，因为文章没有question这个态度；C选项的topic在于difference，但是文章没有分析不同点；E不是文章的主旨，而是Wiehle的关注点；A错在文章并没有解决这个问题；B选项符合文章的主旨和结构
当前版本由 VERNA 更新于2018-05-09 17:47:36 感谢由 VERNA 对此题目的解答所做出的贡献。

选 B 不选 A 是因为文章给出了 A 的答案
当前版本由更新于2018-04-12 15:36:15 感谢由对此题目的解答所做出的贡献。

在对蜘蛛演化的研究中，一个饶有兴趣的问题是，圆形蜘蛛网（orb　web）的编织是否仅经过一次演化，还是经过多次演化。在已知的35,000种蜘蛛中，约一半数量的蜘蛛都要织网，而在织网的蜘蛛中，又有三分之一的蜘蛛编织圆形蜘蛛网。既然绝大部分编织圆形蜘蛛网的蜘蛛要么属于圆蛛科（Araneidae），要么属于虫无蛛科（Uloboridae），所以，圆形蜘蛛网的起源只能通过弄清此两科蜘蛛是否互有联系来确定。
　　　最近，对这两科蜘蛛的某些单个蜘蛛的分类学分析表明，这两科蜘蛛是从不同的原种演化而来的，从而与威勒（Wiehle）的理论相背悖。（威勒的）这一理论假设，这两种蜘蛛必有联系，其根据是这样一种假定，即诸如蜘蛛网这类复杂行为只能经由一次演化过程。按库尔曼（Kullman）的研究，蛛网结构是唯一的一个特征，能暗示出两科蜘蛛之间的联系。两科蜘蛛本身在外表特征、体毛结构、以及眼睛安排这些方面互不相同。唯有虫无蛛科蜘蛛缺乏毒腺。对这两类蜘蛛独特的特征作进一步的辨认和研究，无疑能解答圆形蜘蛛网的演化问题。