The Lowest Point on the Average Total Cost Curve Is

The lowest point on the average total cost curve is where the marginal cost of producing one:

A) more of a good pulls down average total cost due to decreasing marginal costs.
B) less of a good pulls down average total cost.
C) more of a good switches from pulling down average total cost to pulling up average total cost.
D) more of a good drives up average total cost.