Final answer:
The government of Rome transitioned from a republic, where citizens elected leaders such as consuls and senators, to an empire, which is akin to a form of monarchy, in the 1st century B.C.E.
Step-by-step explanation:
The government of Rome switched from a republic to an empire in the 1st century B.C.E. The correct option is 'a. Republic.'
The Roman Republic
The Roman Republic was characterized by a system where leaders were elected and served a defined term in office. For instance, the assembly, known as the Centuriate Assembly, was elected by citizens to create laws, while consuls were annually elected to oversee the laws and ensure their enforcement. Despite their immense power, consuls had their authority checked by short terms and the requirement to counterbalance each other as necessary. In addition, the Senate played a crucial role, acting as a body of aristocratic administrators managing state finances. The Senate's influence, however, fluctuated throughout the history of Rome.
Roman Empire
Following the republic, the system evolved into an empire, expanding Rome's territorial control and altering the nature of its governance, ultimately leading to an imperial rule which is a form of monarchy.