The correct answer is: A. From top to bottom at the lowest point.
The marginal cost curve intersects the average cost curve at the lowest point of the average cost curve. This is because the marginal cost is the additional cost of producing one more unit of output, while the average cost is the total cost divided by the number of units produced. When the marginal cost is less than the average cost, the average cost is decreasing. When the marginal cost is equal to the average cost, the average cost is at its minimum point. When the marginal cost is greater than the average cost, the average cost is increasing.
Here is a diagram that illustrates the relationship between the marginal cost curve and the average cost curve:
[Diagram of a marginal cost curve and an average cost curve intersecting at the lowest point of the average cost curve]
The marginal cost curve is the blue line, and the average cost curve is the red line. The marginal cost curve intersects the average cost curve at the point where the average cost curve is at its lowest point.
I hope this explanation is helpful! Let me know if you have any other questions.