Answer:
d. equals the dollar amount of outstanding U.S. Treasury bonds
Step-by-step explanation:
The National debt is entirely represented by the total dollar amount of outstanding U.S. Treasury bonds, both those bonds that are held by the public (private citizens), or by other governments.
Currently, the U.S. National Debt is over 24 million, and the amount of debt that can be issued in the form of U.S. Treasury bonds is limited by the national debt ceiling.