What Is True About a Minimum Efficient Scale

What is true about a minimum efficient scale?

A) It shows the optimal quantity for a company to produce.
B) It can be most efficiently maintained in large industries by increasing the level of production.
C) It proves that the costs per unit decrease with increases in volume till they reach and then maintain the minimal level.
D) It can be achieved by large industries during economic downturns because they can easily spread their fixed costs when demand declines.