Concept:In the long run, no factor of production is fixed, so a firm can vary all of its costs.
Explanation:The long-run equilibrium position is a period long enough for the firm to adjust every input.
This means land, labour, capital and entrepreneurship can all be changed.
There are no fixed costs in the long run because the firm can expand or contract its scale of operations.
A firm can build a new factory, hire more workers, adopt new technology, or even exit the industry.
Therefore, all costs — both fixed and variable — are variable in the long run.
This flexibility allows the firm to reach the most efficient scale and earn normal profit.
Answer:B. all costs can be varied.