You will be given a definition of a task first, then some input of the task.
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 long had HMCyS Gajabahu been in commission when de Silva became the commanding officer? Passage:In 1953 he was commissioned to the rank of sub lieutenant after completing basic training, after which he was elevated to the rank of lieutenant in 1955, and lieutenant commander in 1963. From 1969 to 1970 he was the defence attache, at the Sri Lanka High Commission in London before being promoted to commander in November 1970, after which he was the commanding officer HMCyS Gajabahu the flagship of the fleet and the co-ordinating officer of the Polonnaruwa District during the 1971 Insurrection. He was the Naval Officer-in Charge of Trincomalee when he was promoted to the rank of captain in 1973, after which he was the Master of MV Lanka Kanthi of the Ceylon Shipping Corporation before becoming chief staff officer (operations). He went on to serve as the co-ordinating officer TAFII (East) and Director Naval Operations when on February 4, 1978, he was made commodore. On July 1, 1979, he assumed duties as the chief of staff at Naval Headquarters, SLNS Ranagala, after which he was promoted to the rank of rear admiral. In June 1983 he was made Commander of the navy, a post he would hold till his retirement at the age of 55, on 1 November 1986, at which point he became the first Sri Lankan officer to be elevated to the rank of vice admiral in the Sri Lanka Navy. Simultaneously acting as the commander-in-chief of the Joint Services Special Operations Command Headquarters established in Vavuniya.
Links: a. Lieutenant b. SLNS Gajabahu c. Polonnaruwa District d. SLNS Gajabahu
Output:
b