At the Time Fisher Corporation Became a Subsidiary of Ashbury

At the time Fisher Corporation became a subsidiary of Ashbury Corporation, Fisher switched depreciation of its plant assets from the straight-line method to the sum-of-the-years'-digits method used by Ashbury. With respect to Fisher, this change was a

A) change in an accounting estimate.
B) correction of an error.
C) change in accounting principle.
D) change in the reporting entity.