下面是小编整理的，希望对大家有帮助。
We sometimes think humans are uniquely vulnerable to anxiety, but stress seems to affect the immune defenses of lower animals too. In one experiment, for example, behavioral immunologist免疫学家 Mark Laudenslager, at the University of Denver, gave mild electric shocks to 24 rats. Half the animals could switch off the current by turning a wheel in their enclosure, while the otherhalf could mot. The rats in the two groups were paired so that each time one rat turned the wheel it protected both itself and its helpless partner from the shock. Laudenslager found that theimmune response was depressed below normal in the helpless rats but not in those that could turn off the electricity. What he has demonstrated, he believes, is that lack of control over anevent, not the experience itself, is what weakens the immune system.
Other researchers agree. Jay Weiss, a psychologist at Duke University School of Medicine, has shown that animals who are allowed to control unpleasant stimuli don’t develop sleep disturbancesor changes in brain chemistry typical of stressed rats. But if the animals are confronted with situations they have no control over, they later behave passively when faced with experiences theycan control. Such findings reinforce psychologists’ suspicions that the experience or perception of helplessness is one of the most harmful factors in depression.
One of the most startling examples of how the mind can alter the immune response was discovered by chance. In 1975 psychologist Robert Ader at the University of Rochester School of Medicineconditioned 使形成条件反射 mice to avoid saccharin 糖精 by simultaneously feeding them the sweetener and injecting them with a drug that while suppressing their immune systems caused stomach upsets.Associating the saccharin with the stomach pains, the mice quickly learned to avoid the sweetener. In order to extinguish this dislike for the sweetener, Ader reexposed the animals tosaccharin, this time without the drug, and was astonished to find that those mice that had received the highest amounts of sweetener during their earlier conditioning died. He could onlyspeculate that he had so successfully conditioned the rats that saccharin alone now served to weaken their immune systems enough to kill them.
11. Laudenslager’s experiment showed that the immune system of those rats who could turn off the electricity ________.
A was strengthened
B was not affected
C was altered
D was weakened
12. According to the passage, the experience of helplessness causes rats to ________.
A try to control unpleasant stimuli
B turn off the electricity
C behave passively in controllable situations
D become abnormally suspicious
13. The reason why the mice in Ader’s experiment avoided saccharin was that ________.
A they disliked its taste
B it affected their immune systems
C it led to stomach pains
D they associated it with stomachaches
14. The passage tells us that the most probable reason for the death of the mice in Ader’s experiment was that ________.
A they had been weakened psychologically by the saccharin
B the sweetener was poisonous to them
C their immune systems had been altered by the mind
D they had taken too much sweetener during earlier conditioning
15. It can be concluded from the passage that the immune systems of animals ________.
A can be weakened by conditioning
B can be suppressed by drug injections
C can be affected by frequent doses of saccharin
D can be altered by electric shocks
参考答案：BCDCA
The "standard of living" of any country means the average person's share of the goods and services which the country produces. A country's standard of living, therefore, depends first andforemost on its capacity to produce wealth. "Wealth" in this sense is not money, for we do not live on money but on things that money can buy: "goods" such as food and clothing, and "services"such as transport and entertainment.
A country's capacity to produce wealth depends upon many factors, most of which have an effect on one another. Wealth depends to a great extent upon a country's natural resources, such ascoal, gold, and other minerals, water supply and so on. Some regions of the world are well supplied with coal and minerals, and have a fertile soil and a favorable climate; other regionspossess perhaps only one of these things, and some regions possess none of them. The U. S. A is one of the wealthiest regions of the world because she has vast natural resources within herborders, her soil is fertile, and her climate is varied. The Sahara Desert, on the other hand, is one of the least wealthy.
Next to natural resources comes the ability to turn them to use. China is perhaps as well off as the U. S. A. in natural resources, but suffered for many years from civil and external wars,and for this and other reasons was. unable to develop her resources. Sound and stable political conditions, and freedom from foreign invasion, enable a country to develop its natural resourcespeacefully and steadily, and to produce more wealth than another country equally well served by nature but less well ordered. Another important factor is the technical efficiency of a country'speople. Old countries that have, through many centuries, trained up numerous skilled craftsmen and technicians are better placed to produce wealth than countries whose workers are largelyunskilled. Wealth also produces wealth. As a country becomes wealthier, its people have a large margin for saving, and can put their savings into factories and machines which will help workersto turn out more goods in their working day.
1. A country's wealth depends upon______. ,
A. its standard of living
B. its money
C. its ability to provide goods and services
D. its ability to provide transport and entertainment
2. The word "foremost" means______.
A. most importantly B. firstly
C. largely D. for the most part
3. The main idea of the second paragraph is that______.
A. a country's wealth depends on many factors
B. the U. S. A. is one of the wealthiest countries in the world
C. the Sahara Desert is a very poor region
D. natural resources are an important factor in the wealth or poverty of a country
4. The third paragraph mentions some of the advantages which one country may have over another in making use of its resources. How many such advantages are mentioned in this paragraph?
A. 2 B. 3
C. 4 D. 5
参考答案：1. C 2. A 3. A 4. B
