What is an example of a bound morpheme?

A bound morpheme is a type of morpheme that cannot stand alone as a word and must attach to a root or base word to convey meaning. The prefix "un" is a classic example of a bound morpheme because it cannot function independently; it requires a base word to create meaning, such as in "unhappy" or "undo." In these cases, "un" modifies the meaning of the root word, indicating negation or opposition.

In contrast, the other choices represent free morphemes, which can exist independently as words. "Fire" and "book" are standalone words that do not need additional morphemes to have meaning. "Children" is also a free morpheme as it functions as a complete word indicating multiple young humans. Therefore, "un" is correctly identified as a bound morpheme due to its dependence on a root for meaning.