Concept:Vertical integration is the combination of businesses operating at different stages of the production or distribution chain.
Explanation:A trust is an association of rival firms in the same industry that combine under one board. It is horizontal, not vertical.
A cartel and a price ring are loose agreements among independent producers to fix prices or limit output, not integrations of production stages.
A merger is the legal joining of two or more firms into one organisation.
When the firms involved operate at different stages — such as a manufacturer merging with its supplier or its distributor — the merger achieves vertical integration.
Therefore, among the given options, vertical integration is best represented by a merger.
Answer:C. Merger