Final answer:
The basic disagreement between Republicans and Democrats in the modern political system is over the responsibilities of government, with issues such as voter participation, special interest politics, and public policy playing key roles.
Step-by-step explanation:
In the modern political system, the issue that represents a basic disagreement between Republicans and Democrats is A. THE RESPONSIBILITIES OF GOVERNMENT. This disagreement is clear from a variety of perspectives, including voter participation and the influence of special interest politics on policymaking. Both parties have evolved over the years, and their current stances reflect a significant divide on several public policy issues and the role of government in society.
For example, Pew Research has documented that Republicans and Democrats have divergent views on government regulation of business, with Republicans generally favouring less regulation and Democrats advocating for more to protect workers and ensure equal opportunities. Over the years, this polarization has grown, indicating a deeper ideological split between the two parties on how much control the government should exert over daily lives and business activities.