题目解析:
C选项定位到倒数第二句many continued to live after their 20 to 25 years of service,符合原文,正确;A选项通过关键词Membership和the reign of the emperor Hadrian定位到第三句,原文中with a peak around A.D. 80,不是选项中的信息,故排除;
B选项定位到倒数第三句Most units raised in Britain went elsewhere on the European continent,信息与原文相反,故排除;D选项的neighboring province原文并未提及,排除。