Text 4 Visiting Oxford Street,a rwd fiUing wilh tatty shop,and overcrowded with people,is plainly a trial.Less plainly,levels of nitrogen dioxide（NO2）,a noxious gas,have been found to be around three times higher there Lhan the legal limit.In 2013 the annual mean concentration of N02 0n the street was one of the highest levels found anywhere in Europe.British air is far cleaner than it was a few decades ago.Fewer people use coal-burning stoves;old industrial plants have been decommissioned.But since 2009 levels of nitrogen oxides and particulate matter,coarse or fine particles that are linked to lung cancer and asthma,have fallen more slowly.The exact iiumber of deaths caused by dirty air is unknown.But in 2010 a govemment advisory group estimated that removing man-made fine particulate matter from the atmosphere woulcl in crease life expeclancy for ihose born in 2008 by an average of six months.Much of the slowdown is the result of fumes from diesel cars,which were championed by successive governments because they use less fuel and thus produce less carbon dioxide than petrol cars.In 2001 0nly 14%0f all cars ran on diesel;by 2013 the proportion had increased t0 35%.（Greener"hybrid"and elecLric cars have increased nine fold since 2006,but account for just 0.5%of the entire fleet.）Second-hand cars are particularly noxious,but even newer ones have not been as clean as hoped.Many cars that let out few pollutants in tests procluced more on the roads.Government's hesitation has not helped.Part of the problem is that several departmenLs 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 fire drivers.However,some improvements have been made.In 2008 a"low-enussion zone"was created in London,which targets large vans and coaches.A smaller"uhra low-enussion zone"has been proposed for 2020,which would charge all vehicles that are not of a certain standard 12.50 pounds a day.European Comnussion fines for breaching limits may encourage cities to do more.But oLher 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.

Govemments try to reduce air pollution by______

• A.imposing extra taxes on vehicles
• B.setiing"no-emission zone"for cars
• C.cutting iail gas emission of vehicles
• D.encouraging people not to drive cars