The correct answer is C) greenbacks.
During the 1860s the US government used greenbacks in order to fund the Civil War.
The Legal Tender Act of 1862 allowed the Union to Print paper money known as greenbacks to fund the war. On February 5, 1862, Congress passed the Legal Tender Act. For the first time, the federal government printed paper money that was not backed by gold or silver. Government obligated creditors to accept greenbacks at face value. So yes, During the 1860s the US government used greenbacks in order to fund the Civil War.