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  3. Less Is More It sounds all wrong—drilling holes in a piece of wood to make it more resistant to knocks. But it works because

Less Is More It sounds all wrong—drilling holes in a piece of wood to make it more resistant to knocks. But it works because

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问题                             Less Is More
    It sounds all wrong—drilling holes in a piece of wood to make it more resistant to knocks. But it works because the energy from the blow gets distributed throughout the wood rather than focusing on one weak spot. The discovery should lead to more effective and lighter packaging materials.
    Carpenters have known【C1】______centuries that some woods are tougher than others. Hickory, for example, was turned into axe handles and cartwheel spokes because it can absorb shocks without breaking. White oak, for example, is much more easily damaged, 【C2】______ it is almost as dense. Julian Vincent at Bathe University and his team were convinced the wood’s internal structure could explain the differences.
    Many trees have tubular vessels that run【C3】______the trunk and carry water to the leaves. In oak they are large, and arranged in narrow bands, but in hickory they are smaller, and more evenly distributed. The researchers【C4】______this layout might distribute a blow’s energy throughout the wood, soaking up a bigger hit. To test the idea, they drilled holes 0. 65 millimetres across into a block of spruce, a wood with 【C5】______vessels, and found that 【C6】______withstood a harder knock.【C7】______when there were more than about 30 holes per square centimeter did the wood’s performance drop off.
    A uniform substance doesn’t cope well with knocks because only a small proportion of the material is actually【C8】______. All the energy from the blow goes towards breaking the material in one or two places, but often the pieces left【C9】______are pristine(未经破坏的).
    But instead of the energy being concentrated in one place, the holes provide many weak spots that all absorb energy as they break, says Vincent. "You are controlling the places【C10】______ the wood breaks, and it can then absorb more【C11】______, more safely. "
    The researchers believe the principle could be applied to any material—【C12】______example , to manufacture lighter and more protective packaging. It could【C13】______be used in car bumpers, crash barriers and armor for military vehicles, says Ulrike Wegst, 【C14】______ the Max Plank Institute for Mental Research in Stuttgart. But she emphasizes that you’d 【C15】______to design the substance with the direction of force in mind. "The direction of loading is crucial, " she says.
【C7】
选项 A、If
B、Just
C、Only
D、Rarely
答案C
解析 空格所在的句子是一个倒装句，所以应该选only，only when引起主句中主语和助动词(did)倒置。整个句子的意思是：只有当每平方厘米超过30个孔时，木头抵御敲打的表现才变差。故选C。
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