Concept:Trade is the economic activity involving the sale, transfer, or exchange of goods and services between buyers and sellers.
Explanation:The key phrase is "sale, transfer or exchange of goods and services."
Industry refers to the production of goods, not their exchange.
Tariff is a tax imposed on imported or exported goods.
Marketing covers promotion, pricing, and distribution, but not solely the act of exchange.
Trade specifically matches the buying, selling, or swapping of goods and services.
Answer:B. trade