When the operation's sales increase, the cost of variable labor increases, and the variable labor cost percentage is unchanged. So option d. is correct.
Variable labor costs are costs that increase and decrease with production. One good example of a common variable labor cost is the rate of an hourly employee. Several industries rely on variable labor, especially around the shopping holidays. These include manufacturing companies, restaurants and retailers.
Another example of a varible labor cost might be the cost associated with contract workers who respond to things like equipment malfunctions or emergency repairs.
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