Topic: Interchange of Parts of Speech,

Best Answer Explained in Below-:

The question asks for the verb form of the word "rich," which is primarily an adjective used to describe someone or something having abundant wealth or resources. However, to understand how it can transform into a verb, we need to focus on the correct options provided.

Among the options, "enrich" stands out as the only true verb form. The word "enrich" means to make something richer or to enhance its value, often associated with adding nutrients to something or improving quality. For example, one might enrich soil to promote better plant growth.

The other options do not qualify as conventional verb forms:
- "Richen" might suggest a form but is not widely recognized in English as a standard verb.
- "Carich" does not exist in English.
- "Richer" is a comparative adjective used to compare levels of richness, not a verb.

Thus, "enrich" is the correct answer because it directly derives from "rich" and represents an action related to increasing richness or value.