5．Rooftops covered with plants-called"green roofs"-could help fight global warming，scientists now suggest．
Green roofs are growing more popular in cities，with the number of green roofs increasing in the United States．In Germany，widely considered the leader in green roofing，some 12percent of all flat roofs are green，with the German green roof industry growing 10to 15percent annually．
These roofs can reduce heating and air conditioning costs，with a roughly 10percent reduction in natural gas usage and a 2percent drop in electricity use for a typical building．Moreover，green roofs last two to three times longer than standard roofs．They also store storm water，which could otherwise exacerbate（加�。ゝlooding．"They can also bring in birds and butterflies，help improve biodiversity（多樣性），"Rowe said．In addition to taking in pollution and noise，the plants in green roofs naturally absorb carbon dioxide，the leading greenhouse gas behind global warming．However，nobody had measured the potential effect of green roofs on carbon dioxide levels until now．
Scientists at Michigan State University found that replacing traditional roofing materials with green roofs in an urban area the size of Detroit，with a population of about one million，would take in more than 55000 tons of carbon．That is roughly similar to getting rid of a year's worth of carbon dioxide sent out by 10000 mid-sized SUVs and trucks．
The challenges green roofs now face in the United States are something about policy and costs．"The government should not necessarily mandate（強(qiáng)制執(zhí)行） them，but it can provide support for them，just as they do in Germany and elsewhere，"Rowe told Live Science．"And green roofs are more expensive，but only initially．Over time，they're cheaper once you consider their benefits energy-wise．It takes about 11to 14years to break even（不贏不虧）．"
59．Which of the following can be the best title？C
A．Standard Roofs and Green Roofs
B．Green Roofs Are Growing More Popular
C．Green Roofs Help Control Global Warming，Study Finds
D．Advantages of Green Roofs
60．Which of the following is NOT true？B
A．Green roofs can take in the leading greenhouse gas behind global warming．
B．It is easier for green roofs to break than standard roofs．
C．A building with a green roof takes less energy to be heated．
D．Green roofs are of higher building cost．
61．We can learn from the passage thatD．
A．Rowe is not optimistic about the future of green roofs
B．Germany has made it a rule to build green roofs
C．The United States is widely considered the leader in green roofing
D．Green roofs can provide habitats for birds and butterflies
62．The underlined word in the last paragraph is closest in meaning toB．
A．slightly B．a(chǎn)t the beginning C．extremely D．in the end．
