The statement that best explains the differences between the democracy of the Athenian polis and the structure of the Roman Republic is:
The senate of the Roman Republic was composed of wealthy patrician magistrates whereas the Athenian ecclesia and Council of 500 were made up of various citizens drawn by lot from different territories within Athens.
This statement highlights the contrast in the composition and structure of political institutions in both systems, emphasizing the oligarchic nature of the Roman Senate compared to the more inclusive and democratic nature of Athenian political assembly.