Definition: In this task, you're given a question, along with a context passage. The passage will not have a direct answer to the question, but can include some information and a clue for the answer. Assuming you can only obtain information about one entity in the passage, your job is to determine whether information from the passage can be used to answer the question. Indicate your choice as `a` for Yes or `b` for No.
Input: Question: Who was the eldest of Liu's oath brothers? Passage:Liu Bei and his oath brothers Guan Yu and Zhang Fei swore allegiance to the Han Empire in the Oath of the Peach Garden and pledged to do their best for the people. However, their ambitions were not realised as they did not receive due recognition for helping to suppress the Yellow Turban Rebellion and participating in the campaign against Dong Zhuo. After Liu Bei succeeded Tao Qian as the governor of Xu Province, he offered shelter to Lü Bu, who had just been defeated by Cao Cao. However, Lü Bu betrayed his host, seized control of the province and attacked Liu Bei. Liu Bei combined forces with Cao Cao and defeated Lü Bu at the Battle of Xiapi. Liu Bei then followed Cao Cao back to the imperial capital, Xu, where Emperor Xian honoured him as his "Imperial Uncle". When Cao Cao showed signs that he wanted to usurp the throne, Emperor Xian wrote a secret decree in blood to his father-in-law, Dong Cheng, and ordered him to get rid of Cao. Dong Cheng secretly contacted Liu Bei and others and they planned to assassinate Cao Cao. However, the plot was leaked out and Cao Cao had Dong Cheng and the others arrested and executed along with their families.


b