What is the primary function of the suffix 'ing' in verbs?

The suffix 'ing' primarily serves to denote a verb form or process, transforming the verb into its present participle form. This addition allows the verb to convey ongoing actions or conditions, enabling it to function in various grammatical roles, such as forming continuous tenses. For example, in the sentence "She is running," the word "running" indicates an action that is currently happening.

This usage of the suffix is vital for forming gerunds as well, which are verbs that act as nouns, such as in "Swimming is fun," where "swimming" refers to the activity itself. While certain other options mention related aspects, they do not encapsulate the core role of 'ing' as accurately as denoting a verb form or process does. Such understanding aids in grasping how modifications to verbs impact their functionality in sentences.