Their
people keep spending additional units of a particular resource on a want until their marginal benefit is

Explanation:

The correct option is D.

Marginal cost refers to the amount of money it cost a company to produce one more of a particular product while the marginal benefit refers to the benefit that is obtained as a result of producing that one extra product. Profit is maximized when the marginal cost equals the marginal benefits.

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The answer is Not Affected By

Explanation:

The marginal cost is the cost that is assumed when starting the production of an additional unit. Another way to describe the marginal cost is as the variation that is produced in the total cost when one unit increases production. While the marginal benefit is the benefit that is achieved as the result of the production of an additional product. The gain is maximum when the marginal cost is equal to the marginal benefit.