[单选,材料题] German people prefer extensive green roof systems to intensive ones.

问题： [单选,材料题] German people prefer extensive green roof systems to intensive ones. 回答下面的题目: Green Roof ResearchThe concept of green roofs is basically about growing plants on roofs, thus helping to replace the green footprint that had been destroyed due to the construction of the building. Green roofs are the most prevalent( 流行 ) in Germany, which is widely regarded as the leader in green roof research.The green roofs that are used these days can be classified as "extensive" and "intensive" systems. Extensive green roofs use mosses, grasses and herbs, which are tolerant to droughts. These plants do not need much maintenance, can be grown in a layer of substrate ( 土层 ) that can be as shallow as 1.5 inches, and generally are inaccessible to the public. In contrast, a wide range of species of plants are grown on intensive green roofs, such as shrubs ( 灌木 ) and even trees, which require deeper substrate layers, and are usually grown on flat roofs. They need intensive maintenance, and are usually areas that resemble parks which are accessible to people.There are several benefits of adopting green roof technologies. Apart from the obvious psychological and aesthetic (美学的 ) benefits of garden-like environments surrounding you, some of the common economic and ecological benefits are: a reduction in the consumption of energy; air and water purification; recovering green spaces; and the mitigation ( 缓解) of the heat island effect in urban areas.The green roof research that is currently ongoing is focused on evaluating the species of plants that are suitable to be grown on roofs, the methods of propagation ( 繁殖 ) as well as establishment, nutrient (养料 ) and water requirement, substrates, and the quantity and quality of water runoff. The evaluation criteria of plant species are: at what rate they can be established their capacity to withstand invasive weeds; tolerance of cold and heat; tolerance of drought conditions; capacity of persistence and survival.A number of experiments are being conducted on roof platform simulations at various research centers. These sites are generally outfitted with equipment, which are used to measure temperatures at different depths of the growing substrates, and the rate and volume of the runoff of stormwaters from each of the platforms.Green roof technology is representative of a completely new market for landscape contractors, and all roofs that currently exist and the future ones to be constructed are the potential market-a market that is too huge to be overlooked.It is estimated that around 10 percent of the flat roofs in Germany are green. A . RightB . WrongC . Not mentioned