What should be added to a root word that is complete?

The correct choice for what should be added to a complete root word is often related to the type of meaning or grammatical function intended. When looking at the choice of adding "-able," this suffix changes a word into an adjective that means "capable of" or "suitable for." It is commonly used with verbs to create adjectives, indicating that something can be done or is worthy of doing.

For example, if the root word is "read," adding "-able" transforms it into "readable," which indicates that something can be read. This transformation showcases the functionality of the root word while conveying a new meaning that is useful in communication.

The other options—such as "-ing," "-tion," and "-ed"—also serve specific grammatical purposes. "-ing" typically indicates an ongoing action, "-tion" generally turns verbs into nouns (denoting the action or process of something), and "-ed" is often used to create the past tense of verbs. However, when the question is focused on adding a suffix that retains completeness and changes the root to describe a characteristic or quality, "-able" is indeed the most fitting choice.