Which of the following statements regarding amortization is true?

a. cash interest payments on bonds equals interest expense on the income statement when there is amoritization of bond premium

b. amortization of the premium causes the premium on bonds payable account to increase

c. amortization of a premium continues over the life of the bond until the balance in the account is reduced to zero

d. amortization of the premium causes the amount of interest expense to increase

Explain.