When reporting on comparative financial statements, which of the following circumstances should ordinarily cause the auditor to change the previously issued opinion on the prior year's financial statements?

a. The prior year's financial statements are restated following the purchase of another company in the current year.

b. A departure from generally accepted accounting principles caused an adverse opinion on the prior year's financial statements, and those statements have been properly restated.

c. A change in accounting principle causes the auditor to make a consistency modification in the current year's audit report.

d. A scope limitation caused a qualified opinion on the prior year's financial statements, but the current year's opinion is properly unqualified.