Ais a form of government in which the leader is not a monarch and certain citizens have the right to vote.
a. polis
c. dictatorship
b. republic
d. circus maximus

 b. republic

Further detail:

A republic differs from a democracy in that when a government is fully a democracy, that means voting and participation in government by all citizens.  A republic may limit voting and political rights to certain types of citizens.  Many republics in history, for instance, have limited voting rights to those who owned a certain amount of property.  Britain was like that for a long time, and the United States started out that way as well.

We think of the United States today as a democratic republic, because voting rights are granted to all citizens age 18 or older, but voters elect representatives who serve in the government of the republic on their behalf.

its many islands, high mountains, and remote peninsulas isolated population centers.