Answer:
Option (D) is correct.
Explanation:
Given that,
Variable cost of one unit = $3
Variable cost of two units = $6
Marginal cost refers to the cost of producing an additional unit of an output and it is added to the total cost of production.
Therefore,
Marginal cost:
= Variable cost of two units - Variable cost of one unit
= $6 - $3
= $3
Hence, the marginal cost associated with two units of production is $3.