Vertical integration is: a. A firm's ownership of vertically related activities b. A firm's control over its input sources and the distribution of its output c. A firm establishing close relationships with its suppliers and its buyers d. A firm's acquisition of a supplier or one of its buyers

A firm's ownership of vertically related activities

Explanation:

As we know that

There are two types of integration i. e horizontal and vertical

The horizontal integration is the integration in which two or more firms amalgamate dealing in the same type of business i. e their products and the level of production is same

While on the other hand the vertical integration is the integration in which the one firm acquired or purchased another firm dealing in different stages but the production level remains the same

Hence, the first option is correct