"A classic economic example of zero-sum boom" (Paragraph 3) connotes
A. economic slack.
B. continued strength.
C. economic recovery.
D. job security.
The writer mentions the political elements in 19th century opera to illustrate
A. the political messages exposed.
B. the universal recognition of high art.
C. the intended changes in popular art.
D. heroes' and heroines' mental states.
在感染过程的5种表现中，所占比例最低，易识别的是
A. 病原体被清除
B. 隐性感染
C. 显性感染
D. 病原携带状态
E. 潜伏性感染
引起急性出血性结肠炎的病原体是
A. 志贺茵
B. 伤寒沙门茵
C. 新型肠道病毒70型
D. 大肠埃希茵0157型
E. 轮状病毒A组
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