If a state government's defined benefit pension plan's net fiduciary position is not expected to be sufficient to make projected benefit payments, the government should use which of the following rates to discount projected future benefit payments?
a. The rate for 10-year treasury notes.
b. The rate for 20-year, tax-exempt general obligation municipal bonds with an average rating of AA/Aa or higher.
c. The government's marginal borrowing rate.
d. The current average prime bank rate.