When constructing an operating model for a potential investment, a private equity professional must forecast both variable and fixed costs. What is the key difference in approach between forecasting variable costs and fixed costs?

A:Variable costs are forecasted based on historical trends, while fixed costs are set as a constant percentage of sales.

B:Variable costs are forecasted as a function of revenue or production volume, while fixed costs are projected to remain constant or change based on known factors unrelated to sales volume.

C:Both variable and fixed costs are forecasted using the same percentage increase year over year, based on historical inflation rates.

D:Variable costs are assumed to remain constant over time, while fixed costs are forecasted based on production volume.