All the options above, except B, are wrong since, cost is the lower limit of price. There are different kinds of costs including fixed costs, variable costs, and total costs. Fixed costs refer to costs which are independent from the level of production. Variable costs are the ones that vary based on production level. Total costs include both fixed costs and variable costs for a given production level. Average total cost is calculated  by adding fixed cost divided by unit sales to the variable cost. Therefore, the correct answer is B.