The correct answer is C. Roosevelt left the Republican Party because Taft defeated him in Republican primaries after he had already served two terms as a Republican President.
Theodore Roosevelt was the twenty sixth president of the United States from 1901 to 1909, representing the Republican Party.
Roosevelt declined to stand for re-election in 1908, and left the country to travel through Europe and Africa. Upon his return to the United States, he faced the new president William Howard Taft. In 1912 he tried to snatch the Republican nomination from Taft; As he did not succeed, he founded the Progressive Party. In the following elections, Roosevelt managed to be the only candidate of a third party to be in second place in a presidential election in the United States, beating Taft but losing against Woodrow Wilson.