If 12 million pairs of shoes are sold,MC exceeds MB , which means that:

It would be fairer for society to devote more resources to the production of shoes.
Society is currently devoting the efficient quantity of resources to the production of shoes.
It would be more efficient for society to devote more resources to the production of shoes.
It would be more efficient for society to devote fewer resources to the production of shoes.
If 4 million pairs of shoes are sold,MB equals MC , which means that:

Society is currently devoting the efficient amount of resources to the production of shoes.
It would be more efficient for society to devote fewer resources to the production of shoes.
It would be more efficient for society to devote more resources to the production of shoes.
It would be fairer for society to devote more resources to the production of shoes.
The efficient allocation of resources would result in the production of pairs of shoes.