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 many years had the Emperor Haile Selassie been in power when the Derg overthrew his rule in 1974? Passage:The Derg overthrew the Ethiopian Empire and Emperor Haile Selassie in a coup d'etat on 12 September 1974, establishing Ethiopia as a Marxist-Leninist communist state with itself as a military junta and provisional government. Various left-wing, ethnic, and anti-communist opposition groups supported by the United States began armed resistance to the Soviet-backed Derg, in addition to the Eritrean separatists already fighting in the Eritrean War of Independence. The Derg used military campaigns and the Qey Shibir (Ethiopian Red Terror) to repress the rebels. By the mid-1980s, various issues such as the 19831985 famine, economic decline and other after-effects of Derg policies ravaged Ethiopia, increasing popular support for the rebels. The Derg dissolved itself in 1987, establishing the People's Democratic Republic of Ethiopia (PDRE) under the Workers' Party of Ethiopia (WEP) in an attempt to maintain its rule. The Soviet Union ended its support for the PDRE in the late-1980s and the government was overwhelmed by the increasingly victorious rebel groups. In May 1991, the PDRE was defeated in Eritrea and President Mengistu Haile Mariam fled the country. The Ethiopian Civil War ended on 4 June 1991 when the Ethiopian People's Revolutionary Democratic Front (EPRDF), a coalition of left-wing ethnic rebel groups, entered the capital Addis Ababa and overthrew the WEP. The PDRE was dissolved and replaced with the Tigray People's Liberation Front-led Transitional Government of Ethiopia.
Links: a. Soviet Union b. 19831985 famine in Ethiopia c. Haile Selassie d. Demographics of Ethiopia
Output:
c