Final answer:
In the early actions of the Delian League, 'plunder' boosted the 'prestige' and 'popularity' of Athens. The League was transformed from a mutual defensive alliance into an Athenian Empire, leveraging its superior naval force to extract wealth and impose control over the other city-states.
Step-by-step explanation:
In the early campaigns of the Delian League, a significant portion of the resulting plunder flowed back to the member states, thus further increasing the prestige and popularity of Athens. The correct answer to fill in the blanks would be 'a. Plunder; prestige; popularity.' Each member of the Delian League contributed to a mutual fund that was initially intended to support a large navy for the defense against Persian interference. Over time, however, Athens became the dominant force within the League, effectively turning it into the Athenian Empire. As Athens tightened its control over the League, it extracted wealth and exacted political influence over its allied city-states, channeling funds into Athenian projects such as the construction of magnificent temples, including the Parthenon, and supporting Athenian democracy.
Athens's control allowed it to implement political reforms in its territories, such as stationing troops and imposing Athenian law, which ensured the continued flow of funds to support Athens's growth. The League's treasury was eventually moved from Delos to Athens, reinforcing the notion that the League had become an extension of Athenian power.