2. The difference between fixed costs and variable costs is that: a. Variable costs per unit vary within the relevant range, while fixed costs per unit re main b. Variable costs per unit are constant (remain unchanged) within the relevant range, c. Variable costs per unit change in direct proportion to changes in activity, while total d. Variable costs per unit and fixed costs per unit remain constant within the relevant e. None of the above. constant within the relevant range. while fixed costs per unit vary within the relevant range. fixed costs change in direct proportion to changes in activity. range