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[共享题干题]【2013年真题】   （一） New Understanding of Natural Silk's Mysterie     Natursl silk, as we all know, has a strength that manmade materials have long struggled tomatch. In a discovery that sounds more like an ancient Chinese proverb than a materials sciencebreakthrough, MIT researchers have discovered that silk gets its strength from its weakness. Or,more specifically, its many weaknesses. Silk gets its extraordinary durability and ductility froman unusual arrangement of hydrogen bonds that are inherently very weak but that work togetherto create a strong, flexible structure.      Most materials -- especially the ones we engineer for strength - get their toughness frombrittleness. As such, natural silks like those produced by spiders have long fascinated bothbiologists and engineers because of their light weight, ductility and high strength (pound forpOund, silk is stronger than steel and far less brittle). But on its face, it doesn't seem that silksshould be as strong as they are; molecularly, they are held together by hydrogen bonds, whichare far weaker than the covalent bonds found in other molecules.     To get a better understanding of how silk manages to produce such strength through suchweak bonds, the MIT team created a set of computer models that allowed them to observe theway silk behaves at the atomic level. They found that the arrangement of the tiny silknanocrystals is such that the hydrogen bonds are able to work cooperatively, reinforcing oneanother against external forces and failing slowly when they do fail, so as not so allow a suddenfracture to spread across a silk structure.    The result is natural silks that can stretch and bend while retaining a high degree ofstrength. But while that's all well and good for spiders, bees and the like, this understanding ofsilk geometry could lead to new materials that are stronger and more ductile than those we cancurrently manufacture. Our best and strongest materials are generally expensive and difficult toproduce (requiring high temperature treatments or energy-intensive processes).    By looking to silk as a model, researchers could potentially devise new manufacturingmethods that rely on inexpensive materials and weak bonds to create less rigid, more forgiving materials that are nonetheless stronger than anything currently on offer. And if you thought youwere going to get out of this materials science story without heating about carbon nanotubes,think again. The MIT team is already in the lab looking into ways of synthesizing silk-likestructures out of materials that are stronger than natural silk -- like carbcn nanotubes. Super-silks are on the horizon.
单选题第1题If the hydrogen bonds break due to external forces, they break fast.
A.Right
B.Wrong
C.Not mentioned

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