In applying costs using a predetermined overhead rate, the most common allocation base is generally direct labour hours. O a. indirect materials used. O b. direct materials used. indirect labour hours. d. In CVP analysis, an assumption that all costs can be classified as either variable or fixed. O a. one assumption is that costs must be classified as either fixed, mixed, or variable. O b. an assumption is that when one more than one type of product is sold, the sales mix will vary O c. the term cost includes only manufacturing costs. O d. A major benefit of using a contribution ratio format is that variable costs are isolated and can be easily reduced. a. it shows the impact of fixed costs on the sales mix. O b. it supports management's decision on its sales mix. O c. it assists in determining the effect of sales on operating income. O d