Explanation:

• Real cost: Refers to the total resources used in the production process, including raw materials and labor. It is a more comprehensive term.

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• Opportunity cost: This isn't about raw materials and labor directly, but rather the benefits foregone of the next best alternative when a choice is made. It’s more about decision-making.

• Variable cost: These change with the level of output, like the cost of materials or number of labor hours needed.

• Fixed cost: These remain constant regardless of output, such as rent or salaries that don't vary with production levels.