I believe the answer is: - a research paper by a social historian that describes and analyzes African American pop culture in the early twentieth century
- a research paper by a cultural historian that analyzes different jazz styles and how they developed. Economic factors could not be considered as a direct influence of jazz development since there is no proof that jazz is only enjoyed by people on a specific economic power. Because of this, the relevant research should only revolve around the music itself, including the culture and its style development.
A historian is researching how jazz music evolved in the United States in the early twentieth century as a result of the intermingling of African American and European music traditions. I'd say that the two works by other historians that the historian will most likely use to develop a hypothesis on this topic are a research paper by a social historian that describes and analyzes African American pop culture in the early twentieth century and a research paper by a cultural historian that analyzes different jazz styles and how they developed.
Thoreau moved to the woods of Walden Pond to learn to live deliberately. He desired to learn what life had to teach him. He moved to the woods to experience a purposeful life.
Sixteen is quadruple the size of four. Quadruple simply means "four times the amount," so if you add four onto itself four times, you reach sixteen. Triple means "three times the amount".