理工類
　　一級重點 Seeing red Means Danger Ahead (C級)
　　The color red often means danger —— and by paying attention, 1 can be prevented. At railroad crossings, flashing red lights warn cars to stay back. A red light at a traffic intersection tells cars to stop, so 2 don't run into other cars.
　　In the future, the color red also may help prevent danger 3 construction sites. Thanks to new work by engineers, bridge supports — or other kinds of materials — could one day contain a color-changing material. It will turn red 4 a structure collapses or falls 5 . A tiny molecule may make a big difference in future warning systems.
　　A polymer 6 a color-changing molecule called a mechanophore turns red seconds before it snaps. The technology may one day allow damage to materials or structures4 to be easily 7 .
　　The secret behind the color-changing material is a particular type of molecule. A molecule is a group of atoms held together by 8 bonds. Molecules come in all shapes and sizes, and make up 9 you can see, touch or feel. How a molecule behaves depends on what kinds of atoms it contains, and how they're held together.
　　When a polymer containing a color-changing molecule called a mechanophore is about to breaks, it produces a color. When a polymer with mechanophore molecules becomes "injured" or 10 , one of the mechanophore bonds breaks and the material turns red. "It's a really simple detection method," says Nancy Sottos, one of the scientists who worked on the project. "We're 11 up this one bond, and it changes color. " Sottos and her team tested the color-changing polymers in their lab. The test 12 proved encouraging.
　　There is a way to get rid of6 the red color: 13 . When a bright light is shone on the mechanophore, the broken bond is fixed7- and the red color disappears. This "self-healing" may be a problem for engineers. They need to use the color-changer in big construction projects that will be 14 , in sunlight. And sunlight will make the mechanophore's warning system useless.
　　 Sottos and her fellow scientists still have 15 work to do before the color-changing molecules can be used outside the lab.
　　練習(xí)：
　　1. A measures B accidents C actions D collap-ses
　　2. A they B it C some D most
　　3. A with B over C at D in
　　4. A before B after C once D while
　　5. A together B behind C down D apart
　　6. A contacting B conducting C containing D considering
　　7. A controlled B spotted C repaired D changed
　　8. A technical B electronic C physical D chemical
　　9. A everything B something C nothing D anything
　　10. A weak B strong C tough D soft
　　11. A using B opening C turning D finishing
　　12. A laws B theories C tools D results
　　13. A air B electricity C light D sound
　　14. A aside B beside C inside D outside
　　15. A a part of B a pair of C a piece of D a lot of

　　答案：BACAD CBDAA BDCDD　　

　　看見紅色意味著危險在前方
　　紅色常常表示危險，通過引起注意能夠防止意外。在鐵路交叉口，閃爍的紅燈警告車輛靠后。在交通十字路121的紅燈告訴車輛停止前進，所以就不會發(fā)生車禍。
　　在未來，建筑工地的紅色可能也可以防止危險。多虧了工程師的新作和橋梁支柱等其他的材料，它們有一天能包含一種會變換顏色的物質(zhì)，該物質(zhì)能夠在建筑物倒塌或之前變成紅色。一個小小的分子就會對報警系統(tǒng)起到很大影響。
　　一個聚合物包含一種變換顏色的分子叫做機械響應(yīng)性聚合物，它能夠在在聚合物斷裂前幾秒鐘變成紅色。這項技術(shù)能夠很容易地發(fā)現(xiàn)材料或建筑物的損壞。
　　這個變換顏色的物質(zhì)的秘密就是一種特別的分子。一個分子是由化學(xué)鍵把一群原子組合起來。分子有各種各樣的形狀和大小，所以能夠組成你所見到的、摸到的和感覺到的任何東西。一個分子怎樣表現(xiàn)取決于它包含什么樣的原子，和他們被怎樣組合起來。
　　當(dāng)包含變換顏色分子的機械響應(yīng)性聚合物要斷裂的時候，它會產(chǎn)生一種顏色。當(dāng)一個包含機械響應(yīng)性聚合物分子的聚合物“受損害”或者變?nèi)醯臅r候，其中的一個機械響應(yīng)性聚合物鍵破碎，這個物質(zhì)變成紅色。“這是一個很簡單的檢測方法。”Nancy Sottos說，她是為這個項目工作的科學(xué)家之一。Sottos和她的團隊在他們的實驗室測試這種變換顏色的聚合物，測試的結(jié)果非常鼓動人心。
　　有一種方法可以除去紅色：光。當(dāng)強光照射在機械響應(yīng)性聚合物上，斷裂的鍵被修復(fù)——紅色就會消失。這種“自我修復(fù)”或許給工程師們帶來問題。他們需要在露天的，也就是暴露在陽光下的大建筑工程外面使用換色器。陽光會使機械響應(yīng)性聚合物的報警系統(tǒng)不起作用。
　　要讓這些變色分子在實驗室以外也能使用，Sottos和她的同事們還有許多工作要做。