Respuesta :
I believe it is A.) Countries involved in trade may have different currencies.
The answer would be A. Process of elimination indicates that answer B is wrong because if they do not do business with other countries then they are not in the trade system. Answer C is incorrect because it involves countries not taking currency from other countries which contradicts the purpose of an international currency exchange system. Finally, letter D is incorrect because while it makes sense, it is arrogant and completely irrelevant since they can not use other countries currency in their home country anyway due to the different values.