填空题 For this study, _____ analyzed the component of air pollution known as fine particulate matter (PM2.5)—the tiny pieces of solid or liquid pollution emitted from motor vehicles, factories, power plants, fires, and smoking. (investigate)无
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【正确答案】 1、investigators    
【答案解析】根据句型可知设空处缺少主语， 由句意推断主语为相关职业的人， 故用investigate的名词复数形式 investigators。