The contribution margin per unit is the difference between the selling price and the variable cost per unit, and the contribution margin ratio is the ratio of the contribution margin to the selling price per unit. If the selling price and the variable cost per unit both increase 10 percent and fixed costs do not change, what is the effect on the contribution margin per unit and the contribution margin ratio? a. Contribution margin per unit and the contribution margin ratio both remain unchanged. b. Contribution margin per unit and the contribution margin ratio both increase. c. Contribution margin per unit increases and the contribution margin ratio decreases. d. Contribution margin per unit increases and the contribution ratio remains unchanged.