In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: How many people lived in Milan when Diocletian restored political stability after the Crisis of the Third Century? Passage:During the Crisis of the Third Century the Roman Empire nearly collapsed under the combined pressures of invasions, military anarchy and civil wars, and hyperinflation. In 284, emperor Diocletian restored political stability. He carried out thorough administrative reforms to maintain order. He created the so-called Tetrarchy whereby the empire was ruled by two senior emperors called Augusti and two junior vice-emperors called Caesars. He decreased the size of the Roman provinces by doubling their number to reduce the power of the provincial governors. He grouped the provinces into several dioceses (Latin: diocesis) and put them under the supervision of the imperial vicarius (vice, deputy), who was the head of the diocese. During the Crisis of the Third Century the importance of Rome declined because the city was far from the troubled frontiers. Diocletian and his colleagues usually resided in four imperial seats. The Augusti, Diocletian and Maximian, who were responsible for the East and West respectively, established themselves at Nicomedia, in north-western Anatolia (closer to the Persian frontier in the east) and Milan, in northern Italy (closer to the European frontiers) respectively. The seats of the Caesars were Augusta Treverorum (on the River Rhine frontier) for Constantius Chlorus and Sirmium (on the River Danube frontier) for Galerius who also resided at Thessaloniki.
Links: a. Milan b. Danube c. Sirmium d. History of Trier
a