Which of the Following Statements Is Correct

Which of the following statements is correct?

A) Average total cost is the difference between average variable cost and average fixed cost.
B) Marginal cost measures the cost per unit of output associated with any level of production.
C) When marginal product rises, marginal cost must also rise.
D) Marginal cost is the price or cost of an extra variable input (for example, an additional worker or machine) divided by its marginal product.