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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

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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.
A spider conserves its energy ______.
选项 A、because it constructs new webs daily
B、as it walks over the strands it lays
C、by eating its own web protein and then re-using it in the new web
D、by eating only in the evening
答案C
解析 作者在第三段第一和第二句中介绍说："The spider conserves energy by recycling web protein．It simply eats its own web each evening and re-uses it to manufacture new silk"，可见C 是正确答案。而A ，B 和D 均不确切。
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