Instructions: 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.
Input: Question: How many years did the ruler of the Sasanian Empire when it had confrontations with the Chionites rule the empire? Passage:Early confrontations between the Sasanian Empire of Shapur II with the nomadic hordes from Central Asia called the "Chionites" were described by Ammianus Marcellinus: he reports that in 356 CE, Shapur II was taking his winter quarters on his eastern borders, "repelling the hostilities of the bordering tribes" of the Chionites and the Euseni ("Euseni" is usually amended to "Cuseni", meaning the Kushans), finally making a treaty of alliance with the Chionites and the Gelani, "the most warlike and indefatigable of all tribes", in 358 CE. After concluding this alliance, the Chionites (probably of the Kidarites tribe) under their King Grumbates accompanied Shapur II in the war against the Romans, especially at the Siege of Amida in 359 CE. Victories of the Xionites during their campaigns in the Eastern Caspian lands were also witnesses and described by Ammianus Marcellinus.
Links: a. Sasanian Empire b. Xionites c. Xionites d. Xionites
Output:
a