To Estimate a Firm's Cash Flow from Operations,depreciation Is Added

To estimate a firm's cash flow from operations,depreciation is added back to net income.Which of the following is true regarding depreciation?

A) that it Depreciation is an extraordinary expense that is not always deducted when calculating net income and this must be added to net income when calculating a firm's cash flow.
B) Depreciation is not an expense used in calculating net income and thus it must be added back to net income when calculating cash flow.
C) They Depreciation is a noncash charge resulting from the purchase of fixed assets, and is thus added to net income when determining a firm's cash flow.
D) Only amortization is added back to before-tax income when determining a firm's cash flow.