材料1
A Dog's Dilemma
Finding a babysitter while you go out to work is, for example, an inconvenience. For the African wild dog, one of the continent's most endangered carnivores, it's a matter of life and death. New research shows that once packs fall below a certain size, there are not enough animals to both hunt food and stay at home protecting the young. The African wild dog has declined drastically over the past century. Habitual loss, persecution and unexplained outbreaks of disease have all been blamed. Only 3,000 to 5,000 animals remain, and the species is expected to go extinct within decades if the trend continues.
Other large carnivores such as the spotted hyena face similar pressures, yet are not declining. Now Franck Courchamp of Cambridge University has found a reason why. The dog's weakness ies in its social organisation.
Within each pack of up to 20 adults and pups, only the dominant male and female breed. The remaining animals help raise the pups, cooperating to hunt prey and defend the kill from other carnivores.
Because pups can't keep up on a hunt, large packs leave an adult behind to protect them from predators, which include lions and hyenas. But leaving a babysitter also carries costs. A smaller hunting party is less able to tackle large prey and to defend the kill.~ There is also one less stomach in which to carry food back to the den, and one more mouth to feed when they get there.
Courchamp investigated this awkward trade-off by modelling how the costs of a babysitter change with decreasing pack size. This showed that packs of more than five adults should be able to feed all the pups and still spare a babysitter. But with smaller packs, either the hunting or the babysitting suffers, or the animals have to compensate by increasing the number of hunting excursions -- which itself carries a cost to the pack.
Field observations in Zimbabwe supported the model. Packs of five animals or fewer left pups unguarded more frequently than larger packs did. There was also evidence that when they did leave a babysitter, they were forced to hunt more often.
A pack which drops below a critical size becomes caught in a vicious circle, says Courchamp, 2 who is now at Paris-Sud University. "Poor reproduction and low survival further reduces pack size, culminating in failure of the whole pack." And deaths causedby human activity, says Courchamp, may be what reduces pack numbers to below the sustainable threshold. Mammal ecologist Chris Carbone at London's Institute of Zoology agrees. Maintaining the integrity of wild dog packs will be vital in preserving the species, he says.
词汇： carnivore／'ka：nivo：(r)／n．食肉动物 hyena／hai'i：no／n．袋狼
pup／pAp／n．小狗 prey／prei／n，被捕食的动物 ．
predator／'predoto(r)／几捕食者 culminate／'k,xlmmeit／n．告终；达到顶点
integrity／m'tegroti／n．完整 Zimbabwe／zim'ba：bwe#n．津巴布韦
练习：
1． The African Wild dog hasbeen endangered．
A． Right B．wrong C． Notmendoned
2． The spotted hyena is onthe verge of extinction．
A． Right B．wrong C， Not mentioned
3． The remaining lions will die out within decades．
A． Right B，wrong C， Not mentioned
4． The dominant female is always left behind to protect the young．
A． Right B．wrong C， Not mentioned
5． There is a tension between babysitting and hunting．
A. Right B. Wrong C. Not mentioned
6. The size of a pack must be big enough for it to survive.
A. Right B. Wrong C. Not mentioned
7. Steps will be taken to protect the African wild dog.
A. Right B. Wrong C. Not mentioned
练习答案
1A 2B 3C 4B 5A 6A 7C
材料2：
Biodiesel
Yuthachai of Thailand has invented a home-grown alternative to expensive imported diesell, a biodiesel derived from vegetable oil. Biodiesel is winning political backing in Thailand because it uses coconut and palm oil, both of which are in price slumps, and it limits the reliance on overseas petroleum source, which have become increasingly expensive.
Yuthachai, 56, has patented his coconut-oil fuel-making process. He developed his biodiesel 18 years ago, using knowledge he gained from working on a plantation and fixing farm machinery. He now sells his fuel at service stations, but refuses to sell his patent, despite attractive offers from overseas oil firms. He is determined to retain control of his formula and keep it accessible to farmers, so they can make their own fuel.
There are several formulations of biodiesel, but Yuthachai's is one of the most basic, using 20 parts crude coconut oil to one part kerosene. It requires only simple, affordable technology to make and works in unmodified, slow-running engines.
Despite the public interest in biodiesel, the government has been cautious about Yuthachai's fuel. Since there is currently no regulatory system for vegetable-oil fuels, Yuthachai fuel cannot be used in regular vehicles. But farmers and ferry operators are more enthusiastic, buying 700,000 liters a day of biodiesel made from crude vegetable oils to run farm machines and boats. Demand is growing: A liter of biodiesel is 4-6 US cents cheaper than diesel.
According to some scientists, the biodiesel produced from crude coconut oil may not run through engines as easily as diesel, and fatty-acid deposits can damage engines in the long run:. A solution may soon come from using waste cooking oil. An experimental biodiesel plant to refine the waste oil is being built in Thailand. The plant will show the biodiesel-making potential of 60,000 tonnes of waste cooking oil that Bangkok generates daily.
Other Asian countries have beenresearching biodiesel -- Malaysia, and the Phil!ppines for 20 years -- but Thailand is the first country to have public policy supporting its commercialization.
That trend looks like continuing3, with the government in talks with a U.S. company to build a more advanced plant in Thailand. Until that's working, homegrown biodiesels will help boost the fortunes of struggling Thais.
练习：
1 Thailand suffers a lot due to the price slumps of its biodiesel.
A. Right B. Wrong C. Not mentioned 2. Biodiesel is superior in quality to traditional petroleum.
A. Right B. Wrong C. Not mentioned
3. Biodiesel can be made from coconut and palm oil, or from waste cooking oil.
A. Right- B. Wrong C. Not mentioned
4. Malaysia, and the Philippines are the first countries in the world to have public policy supporting the commercialization of biodiesels.
A. Right B. Wrong C. Not mentioned
5. Yuthachai fuel is welcomed by both farmers and ferry operators for its low prices.
A. Right B. Wrong C. Not mentioned
6. Yuthachai, the inventor of biodiesel, is currently the general manager of a US-Thailand joint venture in Bangkok.
A. Right B. Wrong C. Not mentioned
7. It seems that Yuthachai places his fellow farmers' interest before his own.
A. Right B. Wrong C. Not mentioned
练习答案
1C 2B 3A 4B 5A 6C 7A