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 US has more than 100 million existing homes, and it would be __1__ wasteful to tear them all down and __2__ 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 __3__ carbon emissions from a new energy-efficient home to make up for the resources lost by destroying an old one. So in the broadest __4__, the greenest home is the one that has already been built. But at the same time, nearly half of US carbon emissions come from heating, cooling and __5__ our homes, offices and other buildings. "You can't deal with climate change without dealing with existing building," says Richard Moe, the president of the National Trust.
With some __6__, 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 __7__ over time and let in more outside air.
Fortunately, there are a __8__ number of relatively simple changes that can green older homes, from __9__ 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 __10__ property owners from rising power costs.
[A] accommodations
[B] clumsy
[C] doubtfully
[D] exceptions
[E] expand
[F] historic
[G] incredibly
[H] powering
[I] protect
[J] reduced
[K] replace
[L] sense
[M] shifted
[N] supplying
[O] vast
