What suffix is often used to indicate the manner in which an action is performed?

The suffix "-ly" is commonly used to form adverbs from adjectives and indicates the manner in which an action is performed. For example, if you take the adjective "quick," adding "-ly" transforms it into "quickly," which describes how someone moves or acts. This characteristic of the suffix makes it particularly useful for modifying verbs by providing additional context about the action being undertaken.

In contrast, the other suffixes serve different functions: "-ing" is primarily used to form the present participle of verbs (like "running"), "-ed" commonly indicates past tense or past participles (such as "jumped"), and "-ness" typically turns adjectives into nouns to describe a state or quality (like "happiness" from "happy"). Thus, "-ly" is the most appropriate choice for indicating the manner of an action.