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  3. Wonder Webs Spider webs are more than homes, and they are ingenious traps. And the world’s best web spinner may be the Golde

Wonder Webs Spider webs are more than homes, and they are ingenious traps. And the world’s best web spinner may be the Golde

admin2011-01-02  57
问题                           Wonder Webs
    Spider webs are more than homes, and they are ingenious traps. And the world’s best web spinner may be the Goldern Orb Weaver spider. The female Orb Weaver spins a web of fibers thin enough to be invisible to insect,  yet【51】 enough to snare a flying bird without breaking.
    The secret of the web’s strength. A type of super-resilient【52】 called dragline. When the female spider is ready to【53】 the web’s spokes and frame, she uses her legs to draw the airy thread out through a hollow nozzle in her belly. Dragline is not sticky, so the spider can race back and forth along【54】 to spin the web’s trademark spiral.
    Unlike some spiders that weave a new web every day, a Golden Orb Weaver【55】 her handiwork until it fails apart, sometimes not for two years. The silky thread is five times stronger than steel by weight and absorbs the force of an impact three times better than Kevlar, a high strength human-made【56】 used in bullet-proof vests.  And thanks to its high tensile strength, or the ability to resist breaking under the pulling force called tension, a single strand can stretch up to 40 percent longer than its original【57】 and snap back as well as new. No human-made fiber even comes【58】.
    It is no【59】 manufacturers are clamoring for spider silk. In the consumer pipeline: high-performance fabrics for athletes and stockings that never run. Think parachute cords and suspension bridge cables. A steady【60】 of spider silk would be worth billions of dollars— but how to produce it? Harvesting silk on spider farms does not【61】because the territorial arthropods have a tendency to devour their neighbors.
    Now, scientists at the biotechnology company Nexia are spinning artificial silk modeled after Goldern Orb dragline. The【62】step: extract silk-making genes from the spiders. Next, implant the genes into goat egg cells. The nanny goats that grow from the eggs secrete dragline silk proteins in their【63】. "The young goats pass on the silk-making gene without【64】help from us," says Nexia president Jeffrey Turner.  Nexia is still perfecting the spinning process, but they hope artificial spider silk will soon be snagging customers【65】the real thing snags bugs.
选项 A、breadth
B、length
C、height
D、strength
答案B
解析 拉伸之后对比的是原长度，可知B．length符合题意。A．breadth宽度：B．length长度；C．height高度；D．strength力度。
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