Final answer:
The Senate had become the central governing body of the Roman state by the end of the second century B.C., exercising significant influence over the Republic's finances and administration.
Step-by-step explanation:
By the end of the second century B.C., the Senate had become the governing body of the Roman state. The Senate was originally an advisory council of elders but evolved to exercise significant authority over state finances and administration during the Republic. This council comprised primarily of aristocratic families advised the consuls, who served as the executives of the Roman Republic. The consuls had considerable powers, including imperium, but their actions could be checked by each other, the law courts, and the Senate itself. While other groups like the Plebeians, Equestrians, and the Consuls played important roles within the Roman political system, it was the Senate that emerged as the central governing body by the late Republic.