Which of the following statements is true?

a. If investors believe inflation will be subsiding in the future, the prevailing yield will be upward sloping.

b. The real rate of interest varies with the business cycle, with the lowest rates seen at the end of a period of business expansion and the highest at the bottom of a recession.

c. The longer the maturity of a security, the greater its interest rate risk.

d. The interest risk premium always adds a downward bias to the slope of the yield.