Final answer:
The sales-volume variance generally arises from the a) unexpected use of more or fewer quantities of variable inputs, such as labor and raw materials.
Step-by-step explanation:
The sales-volume variance is sometimes due to a) unexpected increases in the use of quantities of inputs of raw material. This variance occurs because variable costs, such as labor and raw materials, fluctuate directly with output levels. A greater than planned consumption of materials or labor hours can lead to a negative variance, whereas a lower consumption can result in a positive variance. The other options listed, such as the difference between selling prices, are related to sales price variance or other factors, not specifically to sales-volume variance.