Which of the Following Is $\textbf{ not }$

Which of the following is $\textbf{ not }$ an assumption about the data when using CVP analysis?

A) All costs can be easily and accurately separated into fixed and variable components.
B) Total fixed costs remain at a constant level and variable costs per
C) A linear relationship exists between variable costs and sales activity over the relevant range of interest.
D) Inventory is sold in the period following purchase or manufacture.