Which of the following pairs correctly identifies a morpheme and its function?

The identification of "pre-" as a prefix indicating "before" is an accurate representation of how morphemes function in English. Morphemes are the smallest units of meaning in a language, and prefixes are added to the beginnings of root words to modify their meanings. The prefix "pre-" originates from Latin and is used to convey the idea of something occurring prior to something else, such as in "preview" or "premature." This function aligns perfectly with the definition of a morpheme, making this choice correct.

The other options describe morphemes inaccurately or do not align with their functions. For instance, the suffix "-s" typically indicates plurality, not a subordinate clause. Similarly, "sub-" is a prefix commonly used to denote "under" or "below," not a suffix indicating past tense. Lastly, "re-" serves as a prefix indicating repetition or again, as seen in "redo," rather than denoting opposite action. Therefore, the first choice stands as the best representation of the relationship between a morpheme and its function.