The following data have been collected for four different cost items.

Cost ItemCost at $100$ unitsCost at $140$ unitsW$$8,000$$$10,560$X$$5,000$$ $5,000$Y$$6,500$$ $9,100$Z$$6,700$$ $8,580$

Which of the following classifications of these cost items by cost behavior is correct?

Cost WCost XCost YCost ZA$)$variablefixedmixedvariableB$)$mixedfixedvariablemixedC$)$variablefixedvariablevariableD$)$mixedfixedmixedmixed