How Is the Public Debt Calculated

How is the public debt calculated?

A) By adding up consumption, investment, government purchases, and net exports and then cumulating the annual totals over the years of the nation
B) By subtracting consumption and investment from government spending each year and then cumulating the annual totals over the years of the nation
C) By subtracting current government spending from current government tax revenues
D) By computing the difference between annual government tax revenues and annual government spending and cumulating the differences over the years of the nation