Variable cost per unit.

Answer: Option A

In financial management, variable cost per unit refers to costs that fluctuate in direct proportion to the level of output or production. Therefore, the correct option is A: varies with the level of output. Variable costs typically include expenses such as raw materials, labor, and utilities, which increase or decrease as production levels change.

Option B: remains constant irrespective of the level of output
This option describes a fixed cost rather than a variable cost. Fixed costs remain constant regardless of the level of output. They do not change with changes in production levels.

Option C: changes with the growth of the firm
This option doesn't accurately define variable cost per unit. Variable costs are related to production levels, not necessarily the growth of the firm. They increase or decrease with the quantity of output produced, not necessarily with the overall growth of the firm.

Option D: does not change with volume of production
This option describes a fixed cost rather than a variable cost. Variable costs do change with the volume of production. As more units are produced, variable costs increase, and they decrease when production levels decrease.