根据题干关键词the linguistic insularity可定位到原文第四段第二句“British industry, in particular, has in recent decades often been criticized for its linguistic insularity-for its assumption that foreign buyers will be happy to communicate in English, and that awareness of other languages is not therefore a priority. In the 1960s, over two-thirds of British firms dealing with non-English-speaking customers were using English for outgoing correspondence”，可知在60年代英语的广泛使用存在了一些问题，即英语语言狭隘性的事实。因此，C是正确选项。