阅读理解

     Each year, road accidents kill a million people and injure millions more.The economic costs are

greatest for developing countries.Earlier this year, the United Nations called for a campaign to improve

road safety.

     One way to avoid accidents is better driving.Another is better roads and bridges.Engineers in the

United States have designed ten new concrete mixtures that they think could make bridges last longer.

     Professor Paul Tikalsky leads the experiments by a team at Pennsylvania State University.He says

bridges made of concrete now last about twenty－five to thirty－five years.But he says the new mixtures might extend that to seventy－five or even one－hundred years.

     Concrete is made of stone, sand, water and cement (水泥). The materials in the cement hold the

concrete together.Ancient Romans built with concrete.Yet strengthened concrete bridges did not appear

until the late 1800s.People keep looking for new ways to improve concrete.Professor Tikalsky says it is

one of the most complex of all chemical systems.

     The new mixtures designed by his team contain industrial waste products.He says these make the

concrete better able to resist damage from water and salt over time.One of the products is fly ash.This is

released into the air as pollution when coal is burned.

     Professor Tikalsky says particles (颗粒) of fly ash are almost exactly the same size and chemical

structure as Portland cement.This is the most costly material in concrete.So using fly ash to replace some

of it would save money.

     Over the next two years, engineers will study ten bridges in Pennsylvania.These were built from the

different cement mixtures designed by Professor Tikalsky's team.He says longer－lasting bridges could

save the state more than 35 million dollars a year.And he says the materials would be environmentally

friendly.

     The federal government is paying for part of the research.Engineers anywhere can use the technology.

Professor Tikalsky says some of the ideas have already been put to use in China, the Philippines and

other countries.

1. Why did the United Nations launch the campaign?

A. Because the United Nations wanted to reduce road accidents and economic costs.

B. Because two million people were killed in the accidents.

C. Because engineers wanted to design ten new concrete mixtures.

D. Because the United Nations made bridges of the new mixtures which could last for about

     20 to 35 years.

2. What does the underlined word "This" in the sixth paragraph refer to?

A. Fly ash.  

B. Portland cement.

C. Sand.  

D. Chemical.

3. Which of the following statements is TRUE?

A. Ten new concrete bridges have already been built in the United States.

B. A new concrete bridge could last 50 more years than an ordinary concrete one.

C. People didn't know how to build with cement until the late 1800s.

D. Water and salt won't do any damage to bridges over time.

4. What can we conclude from the passage?

A. Engineers have to pay a lot of money to use the new bridge technology.

B. Pennsylvania State University is paying all the money for the research.

C. Bridges built with fly ash are cheaper than common bridges.

D. Fly ash is much more expensive than Portland cement.

5. What does the passage mainly tell us?

A. The causes of road accidents.

B. The advantages of fly ash.

C. The measures of avoiding road accidents.

D. Latest information about long－life concrete bridges.