Definition: 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: Which submarine did Ian McIntosh serve on first? Passage:He served aboard the submarines HMS Porpoise and HMS Thrasher earning the Distinguished Service Cross for his service in the latter in 1942. As commanding officer of the submarine HMS Sceptre he sank almost 15,000 tons of enemy shipping and took part in Operation Source, the attacks on heavy German warships in Norwegian waters by towed midget submarines. He commanded the submarine HMS Alderney from 1946, the submarine HMS Aeneas from 1950 and then the aircraft carrier in the 1960s. He became Director-General Weapons (Naval) at the Ministry of Defence in 1969 and Deputy Chief of the Defence Staff (Operational Requirements) in 1970 before retiring in 1973.
Links: a. Porpoise b. HMS Sceptre (P215) c. HMS Thrasher (N37) d. HMS Aeneas (P427)
Output:
a