Concept:Internal trade refers to the exchange of goods and services within a country, while some listed factors relate to trade problems and others do not.
Explanation:Natural barriers, such as distance and difficult terrain, can limit trade within a country.
Lack of specialization may reduce the variety of goods available for internal trade.
Bargaining is often part of internal trade, but it can also cause delays or disagreements between buyers and sellers.
Market trade unions, however, are organizations formed by workers to protect their interests and working conditions.
They are not directly responsible for the problems of internal trade.
Answer:B. market trade unions