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  3. To many web-building spiders, most of whom are nearly blind, and the web is their essential window on the world：their means of c

To many web-building spiders, most of whom are nearly blind, and the web is their essential window on the world：their means of c

admin2010-01-15  60
问题      To many web-building spiders, most of whom are nearly blind, and the web is their essential window on the world：their means of communicating, capturing prey, meeting mates and protecting themselves. A web-building spider without its web is like a man marooned on an island of solid rock, totally out of touch and destined to starve to death.
     So vital is the web to an orb-web spider’s survival that the animal will continue to construct new webs daily even if it is being starved. For 16 days the starving spider builds completely normal webs. Then, as the animal gets scrawnier, it constructs a wider-meshed web using fewer strands. Such webs would only trap larger prey, which is more economical from the perspective of a starving spider.
     The spider conserves energy by recycling web protein. It simply eats its own web each evening and re-uses it to manufacture new silk. In studies with radioactively labeled materials, it was found that 95 percent of web protein reappears in the next day’s web. Most of the energy needed for web-building is used in walking over the strands as they are laid down.
     Scientists are impressed by the adaptability of the spider’s highly preprogrammed brain, which is larger for its size than the brain of any other invertebrate. If web-building is interrupted, or if some of the existing strands are destroyed, the spider simply retraces its steps to see where the web is left off and then finishes building a normal web. One spider will even finish building the incomplete web of another.
That a spider is able to finish an incomplete web of another proves that ______.
选项 A、a spider re-uses its web protein to reproduce new silk
B、spiders have a highly preprogrammed brain
C、the web is everything to a spider
D、a spider is able to remedy a destroyed web
答案B
解析 That a spider is able to finish an incomplete web of another，作为第四段中的一个细节是而且应该是为本段主题句服务的，本段的主题句为：(the web-building spiders have)“a highly preprogrammed brain"，由此可以断定B 为正确答案。
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