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) The laissez-faire stance toward trade adopted by first movers
B) Implementation of policies to maximize imports and minimize exports
C) Specializing in the production of goods for which firms have an comparative advantage
D) The 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