Some environmentalists are dubious of the statement that the air quality in this city has ______ since 2000.
【正确答案】 C
【答案解析】一些环境学家对该城市自2000年来空气质量一直恶化这一说法表示怀疑。A. decreed“颁布,命令” B.defaulted“违约,缺席,拖欠”C.deteriorated“恶化,变坏” D.degraded“退化,降级”