阅读理解。
阅读下面短文,根据所读内容在文后第76-85小题的空格里填上适当的单词或短语。
注意：每空不超过3个单词。
The best thing you can say about the roofs of most city buildings is that you don't have to look at them.
That's very good, since an urban landscape viewed from above can be an unlovely thing-block after block
of tarred (铺有沥青的) black rooftops, sticky in summer, ugly year-round. Or at least that's the way it used
to be.
But urban roofs are going green. Environmental 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. The have multiple layers beneath the soil, including a drainage layer, waterproofing,
structural support, and so on. But this system can do a great deal of good. A recent paper in the journal Bio
Science 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.
