Which of the following is true regarding the contribution margin ratio of a company that produces only a single product? Select one: O a. The contribution margin ratio equals the selling price per unit less the variable expense ratio. O b. As fixed expenses decrease, the contribution margin ratio increases. O c. None of the given answer is correct. O d. The contribution margin ratio multiplied by the selling price per unit equals the contribution margin per unit. O e. The contribution margin ratio will decline as unit sales decline