Answer: A) Production expense that changes with the quantity of output produced .
Explanation: Variable cost is that part of 'Total Cost' of output production , which directly varies with the level of output .
Total Cost = Total Variable Cost + Total Fixed Cost
TVC since directly varying with level of output , is zero at zero level of output .
Eg - Cost of Raw Materials , Fuel etc
(This is unlikely Fixed Cost which is not related with output production & isn't 0 at 0 level of income , eg - cost of plant , machine )