Choice "D" is correct. In a statement of cash flows using the indirect method, gain from the sale of used equipment for cash should be reported in operating activities as a deduction from income.
Choice "b" is incorrect. In the investment activities section, cash inflow from the sale should be reported for the entire proceeds from the sale.
Choice "a" is incorrect. In the investment activities section, cash outflows should be reported for purchases of fixed assets, stocks/bonds of other entities.
Choice "c" is incorrect. In the operating activities section, "loss" from the sale of used equipment should be reported as an addition to income.