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  3. Planes may account for only 2 per cent of the world’s carbon emissions, but it is a figure destined to rise. The aviation indust

Planes may account for only 2 per cent of the world’s carbon emissions, but it is a figure destined to rise. The aviation indust

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问题     Planes may account for only 2 per cent of the world’s carbon emissions, but it is a figure destined to rise. The aviation industry is expanding at a dramatic rate, around 5% a year. Twice as many passengers are likely to be passing through British airports in 2020 compared with today, and three times by 2030.
    As the developed world acknowledges climate change warnings, the carbon emissions from other industries will fall. The aviation industry’s output will therefore account for an even larger percentage of emissions. One calculation, by the Climate Change Research(CCR), suggests the U. K. aviation industry could end up accounting for every gram of our carbon quota by 2040. Such calculations suppose aircraft designers cannot clean up their act, a suggestion firmly rejected by experts who point to a massive research program aimed at cutting fuel use by planes by around 50% by 2020, a move that would also halve their carbon emissions.
    To reach that aim, a key factor will be lightweight composites, materials made of several components, including carbon fibers. These are as strong and flexible as metal but as light as plastic. Planes such as the Airbus A340 are already made of material that is 10 per cent carbon composite. This cuts weight, decreases fuel use and reduces carbon emissions. The next generation of aircrafts, will make even more use of composites: a tremendous saving in weight, fuel and carbon.
    Then there is the simple matter of air traffic control. At present, individual countries have their own routes for aircraft crossing their airspaces. "Essentially aircraft travel on doglegs across Europe, and that is very inefficient in terms of fuel use," said Dr. John Green, of the Royal Aeronautical Society. "We need to rationalize air traffic control so that planes fly in straight, energy-efficient lines, an idea that is now being discussed in the EU. "
    Finally, there is aviation fuel. Making it ecologically friendly poses the greatest challenges of all. Biofuels can be used as petrol and diesel substitutes for cars and lorries, but not in planes. "Biofuel is essentially alcohol, and that burns at the wrong temperature for aircraft engines," says Green. "We can use coal to make kerosene, which we could burn in aircraft engines, but that does not help the issue of global warming, of course. " But this does not stop scientists from dreaming. One idea, put forward by the U. S. geneticist Craig Venter last week, would be to create micro-organisms, fitted with artificial chromosomes, which could convert sunlight into fuels that could be burnt in aircraft. These would not involve burning fossil carbon and would be the perfect green fuel. It is still a far-off prospect but realistic, say biologists.
People are using more composites in making aircrafts mainly because
选项 A、composites themselves are very light, strong and as flexible as metal.
B、composites can reduce the plane weight leading to less fuel consumption and carbon emissions.
C、composites can cause less carbon emissions in the process of flying.
D、composites are less expensive than metal.
答案B
解析 人们使用更多的复合材料造飞机，主要是因为[A]复合材料本身非常轻、坚固，并且像金属一样有弹性。[B]复合材料可以减轻飞机的重量，从而降低油耗和减少碳排放量。[C]复合材料能减少飞机飞行过程中的碳排放量。[D]复合材料比金属便宜。根据题干信号词composites可以定位到第三段，[B]符合题意，为飞机使用复合材料的最主要的原因，这也可以在第三段最后两句话中得到验证。[A]是对复合材料的优点的叙述，只是飞机使用复合材料的表面原因，不是最主要的原因。[C]和[D]在文中没有提及，可以很容易排除。
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