Which of the following is an example of a suffix?

A suffix is a letter or a group of letters added to the end of a word to modify its meaning or change its grammatical function. The choice that represents a suffix is "-ing." This particular suffix is commonly used to form the present participle of verbs and can also be used to create gerunds, which allow verbs to function as nouns.

For instance, when added to the verb "run," the suffix transforms it into "running," indicating an ongoing action. In contrast, the other choices represent prefixes, which are added to the beginning of words. "Un-," "pre-," and "dis-" serve to modify the meanings of the root words they precede, but they do not fit the definition of a suffix, which focuses on modifications made at the end of words.