Which was the general purpose currency in pre-colonial Nigeria?

Explanation

In pre-colonial Nigeria, there was a currency used for trading goods and services. The question is asking which currency was used during this time. The options are cowry, salt, cloth, and copper. The correct answer is cowry. Cowry was a type of shell that was used as currency in West Africa for centuries, including in Nigeria. These shells were used for trading and were considered valuable. They were used as a form of currency because they were small, easy to carry, and durable. Other items, such as salt, cloth, and copper, were also used for trading, but cowry was the most widely used currency. It was used for buying and selling goods and services, such as food, clothing, and livestock. Therefore, the correct answer to the question is option A: cowry.