Seeing Red Means Danger Ahead
The color red often means danger - and by paying attention, can be prevented. At railroad crossings, flashing red fights warn cars to stay back. A red light at a traffic intersection tells cars to stop, so dont run into other cars.
In the future, the color red also may help prevent danger construction sites. Thanks to1 new work by engineers, bridge supports2 - or other kinds of materials - could one day contain a color-changing material. It will turn red a structure collapses or falls . A tiny molecule may make a big difference in future warning systems.
A polymer a color-changing molecule called a mechanophore turns red seconds before it snaps3. The technology may one day allow damage to materials or structures4 to be easily .
The secret behind the color-changing material is a particular type of molecule. A molecule is a group of atoms held together by bonds. Molecules come in all shapes and sizes, and make up you can see, touch or feel. How a molecule behaves depends on what kinds of atoms it contains, and how theyre 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 , one of the mechanophore bonds breaks and the material turns red. Its a really simple detection method, says Nancy Sottos, one of the scientists who worked on the project. Were up this one bond, and it changes color. Sottos and her team tested the color-changing polymers in their lab. The test proved encouraging.
There is a way to get rid of~ the red color: . When a bright light is shone on the mechanophore, the broken bond is fixedrn 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 , in sunlight. And sunlight will make the mechanophores warning system useless.
Sottos and her fellow scientists still have work to do before the color-changing molecules can. be used outside the lab.
词汇：
crossing n.十字路口 mechanophore n.机械响应性聚合物 intersection n.交叉路口
molecule n.分子 snap v.折断，断裂 polymer n.聚合物 atom n.原子
注释：
1. Thanks to：多亏，由于
2. bridge supports：桥梁支柱
3. seconds before it snaps：聚合物断裂前几秒钟。Seconds 修饰状语从句 before it snaps。It 指代 polymer。
4. damage to materials or structures：材料或建筑物的损坏。to 是介词。介词短语 to materials or structures 修饰 damage。
5. is about to break：即将断裂。be about to 意为刚刚，行将。
6. get rid of：除去。
7. the broken bond is fixed：断裂的键被修复。Fix 意为修理，修复。
练习：
1 A measures B accidents C actions D collapses
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
答案与题解：
1. B 从第一句的The color often means danger 和...can be prevented所表达 的意思判断，accidents 是答案。因为存在 danger,就有可能出现 accidents。因为有了红 色预警信号，accidents 就有可能 prevented。
2. A 本题的测试点是代词。代词所要指代的词是 cars，它是复数，所以代词 they 是唯一 选择。
3. C construction sites 前面的介词要用 at。with, over 和 in 都不合适。
4. A 这两段说，把一种能变色的化学物质加在建筑材料中，当建筑物断裂之前，变色材料 会显示红色。所以，after 与上下文逻辑相悖。用了 once，句意变成一旦建筑物断裂，变 色材料会显示红色，这不合逻辑，断裂后才变色就是去了预警作用。While 也说不通，因 为It will turn red while a structure collapses的意思是在建筑物倒塌期间，变 色材料会显示红，断裂后才显示红色已经没有意义了。所以，只有 before 才是答案。
5. D 要选 apart。fall apart 意为破碎，破裂。Collapses or falls apart 中的 or
意为即，所以，fall apart 与 collapse 同义。
6. C 从上下文所表达的意思判断，本次要选的词是 containing，即含有。其余三个选项，即 contacting，conducting，considering都与句意搭不上。
7. B 建筑物断裂之前，变色材料会显示红色。这种新技术的预警性很明显，人们见到建筑 物出现红色就知道有险情。所以，spotted是答案。
8. D 本段对变色材料为什么会变色的原理做出解释，句中出现 atoms，molecule 等。所以 变色是一种化学反应，不会是一种物理、电子或技术反应。
9. A 本句的意思是：分子的大小和形状构成世界万物，所以应选 everything。
10. A 本句的意思是：含有 mechanophore 分子的聚合物受伤时，mechanophore 中的一 个键就会断开，于是它便呈现红色。句中的 or 意为即，也就是说，紧接在 or 后面的词 应该是 injured 的同义词，所以要选 weak。
11. B Sottos 和她的研究组进行了实验，断开 mechanophore 的一个键，让其呈现红色。 Opening up 是打开，断开的意思，与上下文意思相符，所以选 opening 是答案。Using up
，turning up或 finishing up与 bond 连用，意思都不对。
12. D 上文说到，Sottos 和她的研究组进行了实验，所以 test 后面的词应该是 results。 最后一个词是 encouraging，也提示了 results 是答案。
13. C 本段第二句说，当明亮的光线射到被断开的化学键上，化学键就会被修复，于是红色
预警信号就消失了。第二句的 light 提示了第一句缺失的关键词就是 light。
14. D 大型建筑物一半均是露天的。句末的 sunlight 提示了要选 sunlight。
15. D 红色预警信号在阳光下是不会出现的。所以，如何能使红色预警信号在室外也能显现 ， 这是科学家今后研究的课题，而且研究的难度和工作量还很大。四个选项中，只有 a lot of 与上下文的意思对得上号。A part of和 a pair of明显不合适。A piece of也不合逻辑。