Given the task definition and input, reply with output. 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: In which country did Trousdell attend school as an officer? Passage:He was Commanding Officer of 1Bn Royal Irish Rangers from February 1989 to August 1991. He attended the Higher Command and Staff Course, graduating in April 1991, and was promoted to colonel on 30 June 1991. From August 1991 to January 1992, he was based in Northern Ireland, overseeing the amalgamation of the Ulster Defence Regiment and the Royal Irish Rangers into the Royal Irish Regiment. He was promoted to brigadier on 31 December 1991, with seniority from 30 June 1991. From January 1992 to November 1993, he was commanding officer of the 48 Gurkha Brigade in Hong Kong. He was posted to the Ministry of Defence from November 1993 until January 1997 as Director of Public Relations (Army).
Links: a. Commanding officer b. Higher Command and Staff Course c. Ulster Defence Regiment d. Ministry of Defence (United Kingdom)
b