At the 30th Unit of Action, the Marginal Benefit Is

At the 30th unit of action, the marginal benefit is equal to $50 and the marginal cost is equal to $40. Which of the following is true?

A) The 30th unit of action should not be undertaken.
B) The 30th unit of action minimizes total costs.
C) The 30th unit of action should be undertaken.
D) The 30th unit of action maximizes total gains (total profits) .