Which of the following statements is most correct?

a) Statement of stockholders equity shows by how much a firm's total assets has changed during the year and why this change occurred.

b) Net operating profit after taxes is profit a company would generate after factoring in interest payments on debt.

c) Free cash flow is the amount of operating income that can be used to pay obligations as well as provide a return to shareholders.

d) Depreciation, a non-cash charge, is the charge to reflect the cost of assets depleted in the production process