Choice "C" is correct. In the relevant range, fixed costs are constant in total, but decrease per unit as production levels increase.
Choice "a" is incorrect. Although total fixed costs are constant in total in the relevant range, the call of the question relates to per-unit fixed costs. Fixed costs per unit decrease as production levels increase.
Choice "d" is incorrect. Variable costs per unit remain unchanged in the relevant range, but increase in total as unit volume increases.
Choice "b" is incorrect. Total variable costs increase as total unit volume increases in the relevant range.
