The long-run average total cost curve:

A) displays declining unit costs so long as output is increasing.
B) indicates the lowest unit costs achievable when a firm has had sufficient time to alter plant size.
C) has a shape that is the inverse of the law of diminishing returns.
D) can be derived by summing horizontally the average total cost curves of all firms in an industry.

Long-Run Average Total Cost Curve

A curve that shows the lowest possible cost of producing different levels of output when all factors of production, including capital, can be varied.

Unit Costs

The investment required by a company to develop, keep, and trade one instance of a specific product or service.

Plant Size

Plant size refers to the capacity or physical extent of a manufacturing or production facility, which impacts its output and efficiency levels.