Read the following citation, and then answer the question.

United States. Cong. Senate. Committee on Entertainment and Music Resources. Hearing on the Impact of Jazz. 110th Cong., 1st sess. Washington: GPO, 2008.

In this citation, “GPO” is

Athe name of the government.
Bthe organization responsible for the research.
Cthe agency that created the document.
Dthe publisher of the document.