The Constitution provides that "a regular Statement and Account of the Receipts and Expenditures of all public Money shall be published from time to time". That provision of the Constitution is made specific by Section 331 of Title 31 of the United States Code. The sums of money reported in the "Statements" are currently being expressed in U.S. dollars (for example, see the 2009 Financial Report of the United States Government). The U.S. dollar may therefore be described as the unit of account of the United States.

Answer this question, if possible (if impossible, reply "unanswerable"): What is the unit of account of the United States?
U.S. dollar