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: How long was Shah Mohammad Reza Pahlavi in power? Passage:In 1961, Sadegh Tabatabai went to Aachen to study biochemistry and later received his doctorate from the University of Bochum. While in Aachen, he organized a student group that campaigned against Shah Mohammad Reza Pahlavi. In 1967, he handled Ulrike Meinhof material about Iran, which was used in a famous column in Konkret magazine opposing the Shah's visit to West Germany that year. Tabatabai gave a speech at the grave of Benno Ohnesorg, an unarmed university student who was shot during a demonstration against the Shah's visit to the Deutsche Oper in Berlin by Karl-Heinz Kurras, a police officer later discovered to be an agent of the East German secret police, the Stasi.
 Links: a. Mohammad Reza Pahlavi b. Death of Benno Ohnesorg c. Deutsche Oper Berlin d. Death of Benno Ohnesorg

a