单选题
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
other half could not. 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 the immune 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
an event, 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 disturbances or 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 they can 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
Medicine conditioned (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 re-exposed the animals to
saccharin, 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 only speculate that he had so successfully
conditioned the rats that saccharin alone now served to weaken their immune
systems enough to kill them.
单选题
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
【正确答案】
B
【答案解析】
单选题
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
【正确答案】
C
【答案解析】
单选题
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 stomach
【正确答案】
D
【答案解析】
单选题
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
【正确答案】
C
【答案解析】
单选题
It can be concluded from the passage that the immune systems of animals
________.