Which of the following statements is true? (You may select more than one answer.)

a. One minus the contribution margin ratio equals the variable expense ratio.

b. Incremental analysis focuses only on the costs and revenues that change as a result of a decision.

c. Sales commissions based on sales dollars can lead to lower profits than commissions based on contribution margin.

d. If a company’s total sales remain constant, then its net operating income must remain constant even if the sales mix fluctuates.