Which of the Following Creates a Barrier to Subsequent Entries

Which of the following creates a barrier to subsequent entries in an industry dominated by first movers?

A) laissez-faire stance toward trade adopted by first movers
B) iImplementation of policies to maximize imports and minimize exports
C) specializing in the production of goods for which firms have a comparative advantage
D) ability of first movers to benefit from increasing returns
E) decrease in the variety of goods available to consumers and increase in the cost of existing goods