Final answer:
Popular sovereignty means that the government derives its authority from the people, and according to the options provided, (a) people determine how they are ruled is the correct answer. This principle is fundamental to democratic governance where people either directly or indirectly exercise their sovereign authority.
Step-by-step explanation:
Popular sovereignty, as introduced by thinkers such as Cicero and Seneca, refers to the concept that people determine how they are ruled. This means that in a system of popular sovereignty, the government's source of authority comes from the consent of the governed, and it is obligated to represent the will of the people. The best fit among the options provided would be (a) people determine how they are ruled. This concept is central to democratic theories where sovereignty lies with the people who exercise their power either directly or through their elected representatives. Democracy, including its manifestations in modern governments like the United States, is structured upon this principle, where leaders are chosen via a social contract to fulfill the collective will and are accountable to the electorate.