Which of the following best describes the interest and interest rates for under and overpayments of income tax liability?

a. The underpayment rate is higher than the overpayment rate.

b. The interest charged on underpayments is deductible.

c. The interest paid on overpayments is tax-exempt income.

d. The overpayment rate and underpayment rate are generally equal and underpayment interest is not deductible and overpayment interest is taxable.