When we think of green buildings, we tend to think of new ones-the kind of modern, solar-paneled masterpieces that make the covers of architecture magazines．But the US has more than 100 million existing homes, and it would be incredibly to tear them all down and them with greener versions． An enormous amount of energy and resources went into the construction of those houses．And it would take an average of 65 years for the carbon emissions (排放) from a(an) __    _ energy-efficient (节能) home to make up for the lost by destroying an old one． So in the broadest sense, the greenest home is the one that has already been built．But at the same time, half of US carbon emissions come from heating, cooling and powering our , offices and other buildings．'You can't deal with climate without dealing with existing buildings,' says Richard Moe, the president of the National Trust． With some exceptions, the oldest homes tend to be the energy-efficient．Houses built before 1939 use about 50% more energy per square foot than those built after 2000, mainly due to the tiny cracks and gaps that over time and let in more outside . ,there are a vast number of relatively simple changes that can green older homes, from ones like Lincoln's Cottage to your own postwar home．And efficiency upgrades (升级) can save more than just the earth; they can help property owners from rising power . 小题1: A．terrible B．wasteful C．wonderful D．useful 小题2: A．put B．build C．replace D．take 小题3: A．reduced B．increased C．used D．destroyed 小题4: A．old B．fashionable C．new D．beautiful 小题5: A．magazines B．trees C．materials D．resources 小题6: A．nearly B．hardly C．rarely D．mostly 小题7: A．libraries B．schools C．homes D．stores 小题8: A．improvement B．appearance C．stability D．change 小题9: A．most B．really C．very D．least 小题10: A．expand B．narrow C．strengthen D．weaken 小题11: A．dust B．air C．smoke D．water 小题12: A．Oppositely B．Unfortunately C．Fortunately D．Frankly 小题13: A．historic B．worthless C．ordinary D．meaningless 小题14: A．charge B．protect C．punish D．warn 小题15: A．prices B．costs C．businesses D．bargains