Which of the following is a true statement about depreciation as the term is used in financial accounting? Select one: a. Depreciation is the decline in market value of a company's long-term assets as they get older. b. Depreciation is a pool of cash that is accumulated for the purpose of replacing worn-out assets. c. Depreciation is the recognition of an asset's historical cost as an expense in a systematic way. d. All of the above are true