The federal debt can fluctuate from year to year based on the annual deficits and surpluses. Assume that a deficit is represented as a negative number whereas a surplus is represented as a positive number.
How is the federal debt derived? Select the correct answer below:

a. the difference between deficits and surpluses.
b. the product of deficits and surpluses.
c. the quotient of debt and surpluses.
d. the sum of deficits and surpluses