So says matja perc at the university of maribor in slovenia , who has identified the most common words used in 5.2 million books published over five centuries .
Perc used data collected by google for the company 's ngram viewer application a tool that lets users see the changing popularity of certain written words over time .
Another perc poll conducted earlier has ranked singaporeas the most foreigner-friendly and least nationalistic among asian countries .
香港同一间机构早些时候的另一个调查则显示,新加坡最欢迎外国人,最没有民族主义威胁。
For discussions of the variability of these curves and the factors that affect them , see this perc report by a group led by bruce yandle of clemson university and this article in environment , development and sustainability by kuheli dutt of northeastern university .
Alan spielvogel , director of technical services at the national cleaners association , a trade group , says the industry has taken steps over the years to reduce perc pollution , primarily by installing advanced machines .
While the epa mandated that cleaning businesses located in residential buildings phase out perc by the end of 2020 , some states , including california , illinois and new jersey , have sought to end its use sooner and more broadly .