B. Variable cost

Explanation:
The answer is “B. Variable cost” because direct materials fluctuate in proportion to the level of production. Variable costs change as production volume increases or decreases, making direct materials a clear example of a variable cost component.

Run-down of reasoning:

• Direct materials are considered variable costs because the amount used directly depends on the number of units produced. The more units are made, the more materials are needed. Fixed costs remain constant regardless of production levels, while variable costs such as direct materials increase with production.