The best response that explains the impact of Greek and Roman democracies on how the U.S. legislative, judiciary, and executive branches function is:
The writers of the U.S. Constitution took inspiration from Greece and Rome but adapted the ancient ideas to create a mixed government system of their own.
This response accurately reflects the historical context in which the U.S. Constitution was created, acknowledging that the framers drew on concepts from ancient democratic systems while also innovating and adjusting those ideas to fit the needs of a modern republic.