阅读理解.

     The best thing you can say about the roofs of most city buildings is that you don't have

to look at them much. That's very good, since an urban landscape viewed from above can

be an unlovely thing-blockafterblockof tarred(铺有沥青的 ) black rooftops , stickyin

summer. windswept in winter and ugly year-round.Or at least that's the way it used to be.

     But urban roofs are going green. Fnvironmental designers have begun to realize that the

tops of buildings don't have to be wastelands. Indeed, they can be gardens, planted with

grasses,flowers and bushes.

     A planted roof usually comes in one of two varieties : extensive or intensive. The

extensive type is wide and shallow, with a soil depth of less than 8 inches, able to support

smaller plants. The intensive type may be smaller,but it's relatively deeper and home to

larger plants.

     Whatever the design,green roofs are not so simple as ordinary gardens. They have multiple

layers beneath the soil, including a drainagelayer , waterproofing , structuralsupport , andso on.

     But this system can do a great deal of good. A recent paper in the joumal BioScience

tells that green roofs can control temperature , contain water and clean the air. And most

impressively , they can cut heat loss from a building by 50% ,lower air-conditioning costs

by 25% , and reduce the urban-heated-island effect by 2℃.

     Of course,apart from the square feet greened and heat reduced. green roofs are even

more valued since people can gain some psychological comfort simply by having a quiet

place to go. As so often happens,what's good for the planet can also be good for the spirit.

1.________2._________3.__________4.___________5.___________

6.________7._________8.__________9.___________10.__________