When we think of green buildings, we tend to think of new ones – the kind of high-tech, solar-paneled masterpieces that make the covers of architecture magazines. But the U.S. has more than 100 million existing homes, and it would be __47__ wasteful to tear them all down and __48__ 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 __49__ carbon emissions from a new energy-efficient home to make up for the resources lost by destroying an old one. So in the broadest __50__, the greenest home is the one that has already been built. But at the same time, nearly half of U. S. carbon emissions come from heating, cooling and __51__ our homes, offices and other buildings. "You can't deal with climate change without dealing with existing buildings," says Richard Moe, the president of the National Trust.
With some __52__, the oldest homes tend to be the least 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 __53__ over time and let in more outside air.
Fortunately, there are a __54__ number of relatively simple changes that can green older homes, from __55__ 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 __56__ property owners from rising power costs.
A) accommodations B) clumsy C) doubtful D) exceptions E) expand F) historic G) incredibly H) powering I) protect J) reduced K) replace L) sense M) shifted N) supplying O) vast