In Principle, a Tendency for Firms to Congregate in a Single

In principle, a tendency for firms to congregate in a single nation to reap trade-cost advantages related to key inputs located within that nation, thereby yielding a trade advantage for that nation, could result from:

A) internal economies and attainment of minimum efficient scale.
B) external economies and agglomeration.
C) economies of scale and government-erected entry barriers.
D) diseconomies of scale and a first-mover advantage.