题目内容：
根据下列短文，回答题。Wonder WebSpider webs are more than homes, and they are ingenious traps. And the world's best webspinner may be the Goldern Orb Weaver spider. The female Orb Weaver spins a web of fibers thin enough to be invisible to insect prey, 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 falls apart, sometimes not for two yearsl. 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 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 Nexia are apinning 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 grown 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.回答第51空。 A．A tough
B．B soft
C．C large
D．D smooth
参考答案：
答案解析：