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

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 Unites 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 plex 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 .
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 .
【小题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 .
【小题2】What does the underlined word “ this ” in the sixth paragraph refer to ?A．Fly ashB．Portland cementC．SandD．Chemical【小题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 .【小题4】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 accidentsD．Latest information about long-life concrete bridgesA