Considering the historian's use of source material, which interpretation is
most valid?

i think the answer is b.

no one really purchased it themselves, it was all america, they had debates etc.

polisit can also mean a body of citizens. in modern historiography, polis is normally used to indicate the ancient greek city-states, like classical athens and its contemporaries, and thus is often translated as "city-state". the body of citizens came to be the most important meaning of the term polis in ancient greece.