Task: Question Generation
Input (English): The U.S. Constitution provides that Congress shall have the power to "borrow money on the credit of the United States". Congress has exercised that power by authorizing Federal Reserve Banks to issue Federal Reserve Notes. Those notes are "obligations of the United States" and "shall be redeemed in lawful money on demand at the Treasury Department of the United States, in the city of Washington, District of Columbia, or at any Federal Reserve bank". Federal Reserve Notes are designated by law as "legal tender" for the payment of debts. Congress has also authorized the issuance of more than 10 other types of banknotes, including the United States Note and the Federal Reserve Bank Note. The Federal Reserve Note is the only type that remains in circulation since the 1970s.
Output (English): Since the 1970s, what is the only type of note that has remained in circulation?