What does a gerund represent in a sentence?

A gerund represents the -ing form of a verb used as a noun. For example, in the sentence "Swimming is fun," the word "swimming" functions as a noun, even though it originates from the verb "to swim." This noun-like quality is what differentiates gerunds from other verb forms. Gerunds can act as subjects, objects, or complements within a sentence, showcasing their versatility in language.

This characteristic makes option B the correct choice, emphasizing the dual nature of gerunds—they are formed from verbs but serve as nouns in usage. In contrast, the other options do not accurately define a gerund or its function.