题目内容：
Questionsare based on the following passage． British air is far cleaner than it was a few decades ago．Fewer people use coal-burning stoves; old industrial plants have been abandoned．But since 2009 levels of nitrogen oxides and particulate matter, coarse or f'me particles that are linked to lung cancer and asthma ( 哮喘 ), have fallen more slowly．The exact number of deaths caused by dirty air is unknown．But in 2010 a government advisory group estimated that removing man-made free particulate matter from the atmosphere would increase life expectancy for those born in 2008 by an average of six months．
Much of the slowdown is the result of fumes from diesel ( 柴油 ) cars, which were championed by successive governments because they use less fuel and thus produce less carbon dioxide than petrol cars．In 2001 only 14% of all cars ran on diesel; by 2013 the proportion had increased to 35%．Greener "hybrid" and electric cars have increased ninefold since 2006, but account for just 0．5% of the entire fleet．Second-hand cars are particularly toxic, but even newer ones have not been as clean as hoped．Many cars that let out few pollutants in tests produced more when on the roads．
Government irresolution has not helped．Part of the problem is that several departments are responsible for air pollution．This means nobody has taken a lead on it, complains Joan Walley, a Labour MP who chairs an environmental committee that has released a series of damning reports．And few politicians are keen to criticize drivers．Talking to Britons about car ownership is "like talking to an American about hand guns", jokes one air-pollution scientist．
Some improvements have been made．In 2008 a "low-emission zone" was created in London, which targets large vans and coaches．A smaller "ultra low-emission zone" has been proposed for 2020, which would charge all vehicles that are not of a certain standard 12．50 a day．European Commission fines for breaching limits may encourage cities to do more．But other countries are more ambitious: 60 such zones exist in Germany, targeting private cars as well as vans．In December Anne Hidalgo, the mayor of Paris, announced that she wanted to ban diesel cars by 2020．Cities in Denmark and the Netherlands do more to boost cycling．
According to the passage, which of the following statements is true? A．British air was once dirty due to coal burning and industrial gas emissions．
B．Particulate matter is closely related to the levels of nitrogen oxides．
C．Statistics have proved the number of deaths caused by dirty air every year．
D．Life expectancy would be prolonged for everyone if particulate matter is removed．
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