What impact does a prefix have on a word?

A prefix has a significant impact on a word because it helps convey additional meaning. By adding a prefix to the beginning of a word, the meaning is modified or specified in some way, providing context that may alter how the word is understood. For instance, the prefix "un-" added to the word "happy" creates "unhappy," which conveys the opposite meaning. Similarly, "re-" added to "write" forms "rewrite,” indicating the action of writing again. Thus, prefixes are instrumental in expanding the vocabulary and enabling more precise expression.

While other options mention aspects of word formation, they do not accurately capture the primary function of prefixes in contributing to meaning, which is the essence of why option B is the correct choice.