Answer:
Option A is the correct answer because Sextus Tarquinius was indeed one of the kings of Rome. Sextus Tarquinius was the third and youngest son of Lucius Tarquinius Superbus, the seventh and last king of Rome. After the fall of the Roman monarchy, the Roman Republic was established, and the office of the Tribune of the Plebs (option B) was created. However, Sextus Tarquinius did not hold this office. He also was not a follower of Brutus (option C) as he was a member of the Tarquin dynasty and thus an opponent of Brutus, who was instrumental in the establishment of the Roman Republic. Finally, Sextus Tarquinius was not a regent who ruled Rome while Lucius Tarquinius Superbus was away (option D) as he was not a regent but a prince and a general who played a significant role in the history of Rome before being exiled.