For over 300 years, one of the most enduring beliefs among historians of England has been that the character of English society has been shaped by the unique openness of its ruling elite to entry by self-made entrepreneurs (especially newly wealthy merchants) able to buy their way into the ranks of elite society.
This upward mobility (upward mobility: 上进心, 向上倾向), historians have argued, allowed England to escape the clash between those with social/political power and those with economic power, a conflict that beset the rest of Europe during the eighteenth and nineteenth centuries.
Upward mobility was also used to explain England’s exceptional stability since the late seventeenth century (no revolutions, for example), as well as such major events as the development of the most efficient agricultural system in Europe, the making of the first industrial revolution, and the onset of severe economic decline.
我考虑：
1、选项BThey develop in response to particular sets of economic conditions的意思是说，open elites相应于economic conditions的趋势(黑体部分所表示的这些经济现象)，或在economic conditions的背景条件下，而发展。B并不一定强调因为这些趋势，open elites才获得发展。而是表达其同时性。
2、C：They tend to unite some of the powerful groups in a society的意思是说，open elites倾向于团结社会有权势的人群。文章中只是说，open elites的这种晋升产生了消除政/社和经济势力之间矛盾的作用，而不是表达C的意思。C表达的是open elites的特点，而文章中没有说open elites的特性如何。
供参考，请指正。 | 
