Question: Of Thee I Sing: A Letter to My Daughters is a children's book by former United States President Barack Obama, the stories of thirteen Americans are told in the book, including Jackie Robinson, who was an American professional baseball second baseman who became the first African American, to play in which organization?
{'answer': 'Major League Baseball (MLB)', 'supporting_facts': [['Of Thee I Sing (book)', 2], ['Jackie Robinson', 0]]}