On August 1, 2007, a steel bridge in Minneapolis, Minnesota, collapsed（倒塌）, sending people and vehicles into the Mississippi River. Thirteen people died and more than 140 others were injured.

The bridge collapse took place during rush hour -- when a lot of cars and trucks were on the road. Investigators found that undersized（尺寸不足的） metal parts of the bridge simply could not support the heavy load.

Finding hidden cracks and other weak areas in large structures can be the difference between life and death. Researchers in Britain say they have discovered a new way to identify cracks inside metal parts before they fail. Their method involves using sound imaging（声成像技术）.

Anthony Croxford leads the team of scientists at Bristol University. They begin their research by sending hundreds of different ultrasonic waves （超声波）into a structure. Then, they listen and study echoes of the sound waves to identify the smallest cracks.

Anthony Croxford says this method is unlike a purely linear system（纯线性系统）. A linear system creates echoes, or similar versions, of the sound wave sent into the material. In other words, you would hear the same frequency（频率） coming back from the object. However, his system of sending out sound waves returns echoes of different frequencies.

Mr. Croxford tested the system on part of a wing from a passenger airplane, an Airbus A320 aircraft. "By using this new approach we can now pick up a crack close to a hole."

He says the system uses only one piece of equipment to get both a linear and nonlinear image.

The technology could help safety inspectors get more detailed estimates of damage in materials like aircraft parts and bridge supports. The damaged materials could then be replaced before they fail.

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1.What is the purpose of the first paragraph?

A To start the topic.

B To tell you an accident.

C To report latest news.

D To warn you of the danger of a bridge.

解析：选A。A。作者意图题。本文作者先报道07年所发生的事来引出此研究的报导。

2.Using sound imaging can_____.

A find the undersized metal parts of a bridge

B investigate the accident

C find the hidden cracks and other weakness

D support heavy loads on the bridges

解析：选C。C。细节理解题。从第3段可知，使用声成像技术目的是找到金属类结构物件中的裂缝或弱的地方。

3.They identify the hidden cracks and weakness by_____.

A discovering the new way of identifying

B sending sound waves into the materials

C sending different sound waves

D listening and studying echoes of sound waves

解析：选D。D。 细节理解题。文章第4段，他们发射不同的超声波，通过听和研究其回声来鉴别是否有小裂纹。

4.Which of the following statements about the sound imaging method is correct?

A They send out sound waves and receive the echoes of the same frequency.

B They send out sound waves and receive echoes of different frequencies.

C They send hundreds of sound waves into a structure and receive the same echo.

D The sound imaging method is almost the same as a linear system.

解析：选B。B。 细节理解题。第5段，提到此方法与单纯的线性系统不一样的地方就是，他们所收到的不是相同的频率。所以B答案是正确的。

5.What can we know from this report?

A With the help of sound imaging, safety inspectors will find more damage.

B With the help of sound imaging, they can pick up crack holes on an airbus A320.

C With the help of sound imaging, tragedies can be prevented.

D With the help of sound imaging, they can get both linear and nonlinear images.

解析：选C。C。主旨大意题。本报告的目的就是宣告声成像技术的成功。而其目的就是为了减少人类悲剧的再次发生。