解释：句子中有两个插入语，一个是跟在preindustrial Europe之后的which we may define here as Europe in the period from roughly 1300 to 1800,这个插入语的直接作用是解释前面的preindustrial Europe的年代，而起到的客观作用则是把主句中的主语和谓语分割得很远;第二个插入语是在began,for the first time in large numbers, to investingate中间，把一个好好的began to斩为两段。
这句话另外一个难以理解的地方是more of the preindustrial European population than the 2 or 3 percent,表示的是在工业化以前的欧洲人口中超过了那2%到3%的人，亦即占97%到98%的人民群众。
意群训练：In the early 1950's,historians who studied preindustrial Europe (which we may define here as Europe in the period from roughly 1300 to 1800) began,for the first time in large numbers,to investigate more of the preindustrial European population than the 2 or 3 percent who comprised the political and social elite:the kings,generals,judges,nobles,bishops,and local magnates who had hitherto usually filled history books.
