Final answer:
Option B: The economy transformed from a rural, agricultural one to an urban one that embraced industrial production.
Step-by-step explanation:
The summary that most clearly emphasizes the theme of social change in the 19th century is option B: The economy transformed from a rural, agricultural one to an urban one that embraced industrial production. This summary highlights the shift from an agrarian society to an industrialized one, which brought about significant changes in the social and economic fabric of the nation. The development of factories and the rise of industrial production led to the growth of cities and the emergence of a new working class, transforming the way people lived and interacted with each other.