The nation that has a comparative advantage in a particular product will be the only world exporter of that product.

Just because a nation has a comparative advantage in producing a certain product, it does not mean that they will be the only world exporter of that product. Other nations may still choose to produce and export that product, but the nation with the comparative advantage may have a lower cost of production and be able to sell the product at a lower price, giving them a competitive edge in the market.