Which process involves changing the nature or function of something?

The correct choice reflects the process of changing the nature or function of something. To convert implies a significant transition from one state or form to another, often involving a comprehensive change in characteristics. For instance, converting a piece of land from agricultural use to industrial use indicates a fundamental change in its purpose and nature.

While "transform," "alter," and "adjust" also involve changes, they have different connotations. "Transform" generally suggests a more profound or complete change rather than just a change in function. "Alter" often indicates a modification rather than a fundamental change, and "adjust" implies a minor change or tweak rather than a thorough conversion. Therefore, the notion of converting specifically encompasses a more complete change in the essence or use of something, making it the most appropriate choice for this question.