单选题
Seeing Red Means Danger Ahead

The color red often means danger and by paying attention, (51) 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 (52) don't run into other cars.
In the future, the color red also may help prevent danger (53) 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 (54) a structure collapses or falls (55) . A tiny molecule may make a big difference in future warning systems.
A polymer (56) a color-changing molecule called a mechanophore turns red seconds before it snaps. The technology may one day allow damage to materials or structures to be easily (57) .
The secret behind the color-changing material is a particular type of molecule. A molecule is a group of atoms held together by (58) bonds. Molecules come in all shapes and sizes, and make up (59) 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 (60) , 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 (61) up this one bond, and it changes color." Sottos and her team tested the color-changing polymers in their lab. The test (62) proved encouraging.
There is a way to get rid of the red color: (63) . When a bright light is shone on the mechanophore, the broken bond is fixed on 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 (64) , in sunlight. And sunlight will make the mechanophore's warning system useless.
Sottos and her fellow scientists still have (65) work to do before the color-changing molecules can be used outside the lab.

【正确答案】 B
【答案解析】[解析] 从第1句的The color red 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。
【正确答案】 A
【答案解析】[解析] 本题的测试点是代词。所要指代的词是cars，它是复数，所以代词they是唯一选择。
【正确答案】 C
【答案解析】[解析] construction sites前面的介词要用at。with、over和in都不合适。
【正确答案】 A
【答案解析】[解析] 这两段说，把一种能变色的化学物质加在建筑材料中，在建筑物断裂之前，变色材料会显示红色。所以after与上下文逻辑相悖。若用once，句意就变成“一旦建筑物断裂，变色材料会显示红色”，这不合逻辑，断裂后才变色就失去了预警作用。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，变色材料会显示红色”，断裂后才显示红色已经没有意义了。所以只有before正确。
【正确答案】 D
【答案解析】[解析] 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。
【正确答案】 C
【答案解析】[解析] 从上下文所表达的意思判断，这里要选的词是containing，即“含有(变色材料的聚合物)”。其余3个选项，contacting(接触)、conducting(进行)和considering(考虑)，都与句意搭不上。
【正确答案】 B
【答案解析】[解析] 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(发现、认出)是答案。
【正确答案】 D
【答案解析】[解析] 本段对变色材料为什么会变色的原理作出解释，句中出现了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。
【正确答案】 A
【答案解析】[解析] 本句的意思是：各种大小和形状的分子构成世界万物，所以应选everything(每样东西，即万物)。
【正确答案】 A
【答案解析】[解析] 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。
【正确答案】 B
【答案解析】[解析] 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，所以是答案。using up(用完)、turning up(出现)或finishing up(做完)与bond连用，意思都不对。
【正确答案】 D
【答案解析】[解析] 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。
【正确答案】 C
【答案解析】[解析] 本段第2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2句中的light提示了第1句缺失的关键词就是light。
【正确答案】 D
【答案解析】[解析] 大型建筑物一半均是露天的。句末的sunlight提示了答案。
【正确答案】 D
【答案解析】[解析] 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。4个选项中，只有a lot of与上下文的意思对得上。a part of和a pair of明显不合适。a piece of也不合逻辑。