Given the task definition and input, reply with output. In this task, you are given a context, a subject, a relation, and many options. Based on the context, from the options select the object entity that has the given relation with the subject. Answer with text (not indexes).

Context: Joseph Philippe Pierre Yves Elliott Trudeau (; October 18, 1919  September 28, 2000), better known as Pierre Trudeau or Pierre Elliott Trudeau, was a Canadian politician who served as the 15th Prime Minister of Canada from 19681979 and 19801984. He is the 3rd longest-serving Prime Minister in Canadian history (behind William Lyon Mackenzie King and John A. Macdonald), having served for 15 years, 164 days., Sir John Alexander Macdonald (11 January 1815  6 June 1891) was the first Prime Minister of Canada (18671873, 18781891). The dominant figure of Canadian Confederation, he had a political career which spanned almost half a century. He drank heavily, and in 1873 was voted out during the Pacific Scandal, in which his party took bribes from businessmen seeking the contract to build the Pacific Railway. Macdonald's greatest achievements were building and guiding a successful national government for the new Dominion, using patronage to forge a strong Conservative Party, promoting the protective tariff of the National Policy, and building the transcontinental Canadian Pacific Railway. Economic growth was slow during his years in office, as Canada verged on stagnation; many residents migrated to the fast-growing United States. He fought to block provincial efforts to take power back from Ottawa. His most controversial move was to approve the execution of Métis leader Louis Riel for treason in 1885; it alienated many Francophones., William Lyon Mackenzie King (December 17, 1874  July 22, 1950) was the dominant Canadian political leader from the 1920s through the 1940s. He served as the tenth Prime Minister of Canada from 1921 to 1926, 1926 to 1930, and 1935 to 1948. He is best known for his leadership of Canada throughout the Second World War (19391945) when he mobilized Canadian money, supplies and volunteers to support Britain while boosting the economy and maintaining home front morale. A Liberal with 21 years and 154 days in office, he was the longest-serving prime minister in Canadian history. Trained in law and social work, he was keenly interested in the human condition (as a boy, his motto was "Help those that cannot help themselves"), and played a major role in laying the foundations of the Canadian welfare state., The Canadian federal election of 1968 was held on June 25 , 1968 , to elect members of the Canadian House of Commons of the 28th Parliament of Canada . The Liberal Party won a majority government under its new leader , Prime Minister Pierre Trudeau . This was the last federal election in which some provinces ( specifically Manitoba , Nova Scotia , Quebec and Saskatchewan ) had fewer seats they had been allocated in the previous election due to a redistribution . The 1966 census , for example , revealed that Alberta had a population about 50 % greater than Saskatchewan 's even though both provinces had the same number of seats at the time ( 17 ) . Saskatchewan was the only province to lose multiple seats in the redistribution ( 4 ) . It was also the only election in Canadian history where fewer total seats were contested compared to the previous vote ( 264 instead of 265 ) . Changes to the Constitution enacted since that time have rendered the prospect of similar reductions far less likely ., Subject: canadian federal election, Relation: office_contested, Options: (A) prime minister (B) prime minister of canada
prime minister of canada