Concept:A vertical combination occurs when firms at different stages of the same production chain merge.
Explanation:Vertical combination is also called vertical integration.
It brings together businesses that handle a product at different stages, from raw materials to final sale.
Option A involves a spinning firm and a wearing firm.
A spinning firm produces yarn from raw fibre, while a wearing firm uses cloth to make finished clothing.
These are successive stages in the textile industry.
Therefore, their merger is a clear example of a vertical combination.
Options B, C, and D involve firms operating at the same stage of production.
Mergers among such firms are horizontal combinations, not vertical combinations.
Answer:A. a spinning firm and a wearing firm