Which of the following statements is correct?

a. prior year statements should always be restated for changes in accounting estimates.

b. changes in accounting policy are always handled in the current or prospective period.

c. correction of prior period error should be presented as an adjustment on the current income statement.

d. a change from the deferral and amortization method to the immediate recognition method of accounting for defined benefit pension plans should be treated as a change in accounting policy.