题目内容
The main idea of the text is that
查看答案
搜索结果不匹配？点我反馈
更多问题
Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. (40 points)
Prudent investors learned long ago that putting your eggs into lots of baskets reduces risk. Conservationists have now hit on a similar idea: a population of endangered animals will have a better chance of survival if it is divided into interconnected groups. The prospects of the species will be better because the chance that all the constituent subpopulations will die out at the same time is low. And, in the long term, it matters little if one or two groups do disappear, because immigrants from better-faring patches will eventually re-establish the species' old haunts.
One endangered species divided in just this way is the world's rarest carnivore, the Ethiopian wolf, which lives high in the meadows of the Bale Mountains. Just 350 exist in three pockets of meadow connected by narrow' valleys in the Bale Mountains National Park, with a further 150 outside this area.
Two of the main threats to the Ethiopian wolf come from diseases carried by domestic dogs. One of these, rabies, is of particular concern because it is epidemic in the dog population. At first blush, vaccinating the wolves against rabies seems a simple solution. It would be ambitious, because the prevailing thinking—that all individuals matter and therefore all outbreaks of disease should be completely halted—implies that a large proportion of wolves would need to be vaccinated.
Dan Haydon, of the University of Glasgow, and his colleagues believe that conservation biologists should think differently. With the exception of humans, species are important but individuals are not. Some outbreaks of disease can be tolerated. In a paper published this week in Nature, they recast the mathematics of vaccination with this in mind.
On epidemiologists' standard assumption that every individual counts, vaccination programmes are intended to prevent epidemics by ensuring that each infected animal, on average, passes the disease on to less than one healthy animal. This implies that around two-thirds of all the wolves would need to be vaccinated. A programme that sought to save a species rather than individuals would allow each infected wolf to pass the disease on to more than one healthy animal and hence require fewer vaccinations. Dr Haydon and his colleagues have calculated, using data from a rabies outbreak in 2003, that vaccinating between 10% and 25% would suffice, provided veterinarians gave jabs to those wolves living in the narrow valleys that connect the subpopulations.
If the threat of rabies arose every five years, targeting all the wolves in the corridors would cut the risk of extinction over a 20-year period by fourfold. If this were backed up by vaccinating a mere 10% of the wolves in the three connected meadows, the chance of extinction would drop to less than one in 1,000. Saving a few seems to be an efficient way of protecting the many.
By citing prudent investors' idea, the author wants to illustrate that
In a modern factory, the workers feel frustrated in that
Late-night Drinking
Coffee lovers beware. Having a quick "pick-me-up" cup of coffee late in the day will play havoc with you sleep. As well as being a stimulant, caffeine interrupts the flow of melatonin, the brain hormone that send people into a sleep.
Melatonin levels normally start to rise about two hours before bedtime. Levels then peak between 2 a.m. and 4 a.m., before falling again. "It's the neurohormone that controls our sleep and tells our body when to sleep and when to wake," says Manrice Ohayon of the Stanford Sleep Epidemiklogy Research Center at Stanford University in California. But researchers in Israel have found that caffeinated coffee halves the body's levels of this sleep hormone.
Lotan Shilo and a team at the Sapir Medical Center in Tel Aviv University found that six volunteers slept less well after a cup of caffeinated coffee than after drinking the same amount of decaf. On average, subjects slept 336 minutes per night after drinking caffeinated coffee, compared with 415 minutes after decaf. They also took half an hour to drop off--twice as long as usual-- and jigged around in twice as much.
In the second phase of the experiment, the researchers woke the volunteers every three hours and asked them to give a urine sample. Shilo measured concentrations of a breakers were half those in decaf drinkers. The results suggest that melatonin concentrations in caffeine drinkers were half those in decaf drinkers. In a paper accepted for publication in Sleep Medicine, the researchers suggest that caffeine blocks production of the enzyme the drives melatonin production.
Because it can take many hours to eliminate caffeine from the body, Ohayon recommends that coffee lovers switch to decal after lunch.
The author mentions "pick-me-up" to indicate that______.
Diet, Alcohol Linked to Nearly One Third of Cancers
Diet is second only to tobacco as a leading(1)of cancer and，along with alcohol，is responsible for nearly one third of cases of the disease(2)developed countries, a leading researcher said on Tuesday.
Dr. Tim Key, of the University of Oxford, told a cancer conference that scientists are still discovering how certain foods contribute to(3), but they know that diet, alcohol and obesity(4)a major role.
"Five percent of cancers could be avoided(5)nobody was obese," he said.
While tobacco is linked to about 30(6)of cancer cases, diet is involved in all estimated 25 percent and alcohol(7)about six percent.
Obesity raises the(8)of breast, womb, bowel and kidney cancer, while alcohol is known to cause cancers of the mouth, throat and liver. Its dangerous impact is(9)when combined with smoking.
Key told the meeting of the charity Cancer Research UK(10)other elements of diet linked to cancer are(11)unknown but scientists are hoping that the EPIC study, which is comparing the diets of 500, 000 people in 10 countries and their risk of cancer, will provide some(12)
Early results of the study have revealed that Norway, Sweden and Denmark have the(13) consumption of fruit and vegetables among European countries while Italy and Spain have the highest. Eating at(14)five portions of fruit and vegetables a day is recommended to reduce the risk of cancer.
Key, principal scientist on the EPIC study, said it is looking at dietary links to some of the most common cancers(15)colorectal, breast and prostate.
obesity n. 肥胖
bowel n.肠
dietary adj. 饮食的
prostate adj. 前列腺的
obese adj. 肥胖的
womb n.子宫
colorectal adj. 结肠直肠的
微信支付 
支付宝支付