All of the Following,except One,are Reasons Why Complete Free Trade

All of the following,except one,are reasons why complete free trade may not be possible.Which is the exception?

A) Transportation costs might exceed any cost differences between countries.
B) Higher taxes in one country than another might exceed any cost differences.
C) Free trade usually causes a reduction in international competition.
D) Differences in languages and cultures might restrict the amount of trade.
E) Cost differences between countries disappear as one country tries to totally specialize.