题目内容：
根据以下材料，回答题Living on Water
Desperately short of living space and dangerously prone to flooding, the Netherlands plans to start building homes, businesses and even roads on water.
With nearly a third of the country already covered by water and half of its land mass below sea level and constantly under threat from rising waters, the authorities believe that floating communities may well be the future.
Six prototype wooden and aluminum floating houses are already attached to something off Amsterdam, and at least a further 100 are planned on the same estate, called Ijburg.
"Everybody asks why didn't we do this kind of thing before," said Gijsbert Van der Woerdt,director of the firm responsible for promoting the concept. "After Bangladesh we're the most densely populated country in the world. Building space is scarce and government studies show that we'll need to double the space available to us in the coming years to meet all our needs."
Before being placed on the water and moved into position by tugboats (拖船), the houses are built on land atop concrete flat-bottomed boats, which encase giant lumps of polystyrene (聚苯乙烯) reinforced with steel. The flat-bottomed boats are said to be unsinkable and are anchored by underwater cables. The floating roads apply the same technology.
The concept is proving popular with the Dutch. "The waiting list for such homes, which will cost between euros 200,000, 500,000 to buy, runs to 5,000 names," claims Van der Woerdt.
With much of the country given over to market gardening and the intensive cultivation of flowers, planners have also come up with designs for floating greenhouses designed so that the water beneath them irrigates the plants and controls the temperature inside.
A pilot project, covering 50 hectares of flooded land near Amsterdam's Schiphol airport, is planned for 2005.
The opportunities for innovative developers look promising. "We have 10 projects in the pipeline --floating villages and cities complete with offices, shops and restaurants," Van der Woerdt said.
The Netherlands plans to start building floating communities on water because A．most parts of the country are covered by water.
B．the country is constantly threatened by floods.
C．it will promote the cultivation of flowers.
D．people think it better to live on water.
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