Final answer:
The most influential feature of ancient Roman government on the US Constitution is republicanism, a form of representative democracy where citizens elect leaders rather than a direct democracy.
Step-by-step explanation:
Based on the information provided, the feature of ancient Roman government that most influenced the founders in framing the US Constitution was a) Republic. The Roman Republic mixed elements of democracy, aristocracy, and monarchy, but the core idea that the American revolutionaries adopted was republicanism, where citizens elect leaders to make decisions. In the Roman system, citizens voted in legislative assemblies and for consuls, just as the United States established a system where citizens elect representatives. This form of government is different from a direct democracy, where all citizens would directly vote on all decisions, instead establishing a representative democracy.