Which of the Following Is Not an Assumption Associated with Marginal

Which of the following is not an assumption associated with marginal costing and break-even analysis?

A) In marginal costing and break-even analysis it is assumed that cost behaviour is linear
B) In marginal costing and break-even analysis it is assumed that not all costs can be classified as fixed or variable
C) In marginal costing and break-even analysis it is assumed that variable costs per unit remain constant
D) In marginal costing and break-even analysis it is assumed that fixed costs remain constant