confirm with me if im correct please!

The following is true of depreciation accounting. a. It is a cost allocation system, not a measure of market value. ob. It is part of the matching of revenues and expenses. c. There are several methods of calculating depreciation under GAAP. d. All of these. Which statement(s) best describe the treatment of revisions in depreciation estimates? a. Accounted for prospectively b. Accounted for retrospectively c. Considered an error d. All of the above