The statement that best explains the differences between the democracy of the Athenian polis and the structure of the Roman Republic is:
B. 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 accurately highlights the distinction in the political structures. The Roman Senate was predominantly composed of the aristocracy (patricians), while Athenian democracy involved a broader participation of citizens through random selection for positions in the Council of 500 and the Assembly (ecclesia), emphasizing the direct involvement of a wider population in the decision-making process.