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 dont run into other cars.

　　In the future, the color red also may help prevent danger3construction sites. Thanks to new work by engineers, bridge supports- or other kinds of materialscould one day contain a color-changing material. It will turn red 4a structure collapses or falls 5 A tiny molecule may make a big difference in future warning systems.

　　A polymer6 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 7 .

　　The secret behind the color-changing material is a particular type of molecule. A molecule is a group of atoms held together by8bonds. Molecules come in all shapes and sizes, and make up 9you 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 or10, 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 11 up this one bond, and it changes color. Sottos and her team tested the color-changing polymers in their lab. The test12 proved encouraging.

　　There is a way to get rid of the red color: 13. When a bright light is shone on the mechanophore, the broken bond is fixed - 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 mechanophores warning system useless.

　　Sottos and her fellow scientists still have15 work to do before the color-changing molecules can be used outside the lab.

　　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

　　参考答案　　BACAD CBDAA BDCDD

　　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 dont run into other cars.

　　In the future, the color red also may help prevent danger3construction sites. Thanks to new work by engineers, bridge supports- or other kinds of materialscould one day contain a color-changing material. It will turn red 4a structure collapses or falls 5 A tiny molecule may make a big difference in future warning systems.

　　A polymer6 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 7 .

　　The secret behind the color-changing material is a particular type of molecule. A molecule is a group of atoms held together by8bonds. Molecules come in all shapes and sizes, and make up 9you 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 or10, 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 11 up this one bond, and it changes color. Sottos and her team tested the color-changing polymers in their lab. The test12 proved encouraging.

　　There is a way to get rid of the red color: 13. When a bright light is shone on the mechanophore, the broken bond is fixed - 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 mechanophores warning system useless.

　　Sottos and her fellow scientists still have15 work to do before the color-changing molecules can be used outside the lab.

　　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

　　参考答案　　BACAD CBDAA BDCDD