问题
选择题
生态系统多样性形成的原因可以概括为[ ]
A．基因突变和重组
B．自然选择
C．共同进化
D．地理隔离
答案
答案：C
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生态系统多样性形成的原因可以概括为[ ]
A．基因突变和重组
B．自然选择
C．共同进化
D．地理隔离
答案：C
| One day, drought may be a thing of the past, at least in any country not too far from the sea. Vast areas of desert throughout the world may for the first time come to life and provide millions of hectares of cultivated land where now nothing grows. By the end of this century this may not be mere speculation. Scientists are already looking into the possibility of using some of the available ice in the Arctic and Antarctic. In these regions there are vast ice-caps formed by snow that has fallen over the past 50,000 years. Layer upon layer of deep snow means that, when melted, the snow water would be pure, not salty as sea-ice would be. There is so much potential pure water here that it would need only a fraction to turn much of the desert or poorly irrigated parts of the world into rich farmland. And what useful packages would come in! It should be possible to hack off a bit of ice and transport it! Alternatively perhaps a passing iceberg could be captured. They are always breaking away from the main caps and floating around, pushed by currents, until they eventually melt and are wasted. Many icebergs are, of course, much too small to be towed any distance, and would melt before they reached a country that needed them anywhere. It would be necessary to harness one that was manageable and that was big enough to provide a good supply when it reached us. Engineers think that an iceberg up to 11 kilometres long and 2 kilometres wide could be transported if the tug pulling it was as big as a supertanker! Even then they would cover only 32 kilometres every day. However, once the iceberg was at its destination, say at one end of Hong Kong harbour, more than 7,000 million cubic metres of water could be taken from it! That would probably be more than enough for Hong Kong even in the hottest summer! But no doubt a use could be found for it. Apparently, scientists say, there would not be too much wastage in such a journey. The larger the iceberg, the slower it melts, even if it is towed through the tropics. This is because when the sun has a bigger area to warm up, less heat actually gets into the iceberg. The vast frozen center would be unaffected. Even with the giant tug that would have to be available to tow an iceberg seven miles long, the voyage would take many months from the Antarctic to Hong Kong, for example, but as per engines are built and more is known about sea currents, the journey could get shorter and shorter and thus the wastage less and less. Airline pilots have learnt to use jet streams ten miles above the earth to increase speed and save fuel so, surely, a boat towing an iceberg could make use of fast-flowing currents and avoid warmer water. |
According to the passage, which of the following statements is NOT true
A．(A) The time for towing icebergs may be made shorter.
B．(B) It is possible to use ships to tow icebergs from the polar areas.
C．(C) Airline pilots may make use of jet streams to help tow an iceberg.
D．(D) Not too much of the iceberg would melt while being towed through the oceans.