Answer:
C. all factors of production are variable.
Explanation:
The long run is a time horizon where all factors of production are variable. It is usually the planning period of a firm. In the long run a firm can decide to enter or leave an industry, increase or reduce price and adjust cost of production.
The short run is a time horizon where some factors of production are variable, while at least one factor of production is fixed. Usually a firm cannot adjust production, costs or prices in the short run.
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