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1999年6月大学英语六级阅读理解真题及答案免费下载，
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
1999年6月大学英语六级阅读理解真题及答案
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