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 reexposed 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.
1. 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
2. Laudenslagers experiment showed that the immune system of those rats who could turn off the electricity ________.
A) was strengthened
B) was not affected
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