The answer is B. legal systems.
The reunification of East and West Germany involved several steps, and one of the critical aspects was aligning their legal systems. East Germany (GDR) had a socialist legal system, while West Germany (FRG) had a democratic legal framework. When the two Germanys reunified in 1990, a significant task was to integrate the legal frameworks to ensure that the laws and regulations were consistent across the newly unified country.
While governments, populations, and economies also played crucial roles in reunification, the legal system was a foundational aspect that needed to be addressed to ensure coherent governance and citizens' rights in the unified Germany. Therefore, the unification of the legal systems was a prominent first step in the reunification process.