Q: 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: Who was the Han emperor when the Xianbei killed the Xiongnu chanyu Youliu? Passage:The Xianbei (; ) were an ancient nomadic people that once resided in the eastern Eurasian steppes in what is today Mongolia, Inner Mongolia, and Northeastern China. They originated from the Donghu people who splintered into the Wuhuan and Xianbei when they were defeated by the Xiongnu at the end of the 3rd century BC. The Xianbei were largely subordinate to larger nomadic powers and the Han dynasty until they gained prominence in 87 AD by killing the Xiongnu chanyu Youliu. However unlike the Xiongnu, the Xianbei political structure lacked the organization to pose a concerted challenge to the Chinese for most of their time as a nomadic people. After suffering several defeats by the end of the Three Kingdoms period, the Xianbei migrated south and settled in close proximity to Chinese society and submitted as vassals, being granted the titles of Dukes. As the Xianbei Murong, Tuoba and Duan tribes were one of the Five Barbarians who were vassals of the Han Chinese Western Jin and Eastern Jin dynasties, they took part in the Uprising of the Five Barbarians as allies of the Han Chinese Eastern Jin against the other four barbarians, the Xiongnu, Jie, Di and Qiang. The Xianbei were at one point all defeated and conquered by the Di Former Qin empire before it fell apart at the Battle of Fei River at the hands of the Eastern Jin. The Xianbei later founded their own states and reunited northern China as the Northern Wei. These states opposed and promoted sinicization at one point or another but trended towards the latter and had merged with the general Chinese population by the Tang dynasty.
Links: a. Han dynasty b. Battle of Fei River c. Five Barbarians d. Eurasia
A:
a