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: What is the full name for the enforcement body that arrested Ottwalt and his wife? Passage:In 1933, Ottwalt and his wife, Waltraut, left Germany and went into exile in Denmark, then, by way of Czechoslovakia, ended up in the Soviet Union. Living in Moscow, Ottwalt wrote for the German exile magazine Internationale Literatur (published by Johannes R. Becher) and was an editor at Vegaar Bibliothek. He also wrote for the Deutsche Zentral Zeitung. In 1936, he and his wife were ensnared in the Stalinist purges and arrested by the Soviet secret police, the NKVD. He was charged with suspicion of espionage, sentenced to forced labor and deported to a gulag near Archangelsk. His wife was sentenced to forced labor in Kotlas. She was deported back to Germany in January 1941 and didn't learn about his death until January 1958, when the Soviet Red Cross informed her that her husband had died on 24 August 1943.
 Links: a. Deutsche Zentral-Zeitung b. NKVD c. Stalinism d. Gulag

b