What commonly consists of prefixes and suffixes?

The correct answer is affixes, as they specifically refer to morphemes that can be attached to a root word to modify its meaning or create a new word. Affixes include both prefixes, which are added to the beginning of a word, and suffixes, which are added to the end. For example, in the word "unhappiness," "un-" is a prefix that negates the meaning, while "-ness" is a suffix that converts an adjective into a noun.

Interfixes and circumfixes, while related to morphological processes, are more specialized and not as broadly applied as affixes. Interfixes are elements inserted within a word, and circumfixes are affixes that attach to both the beginning and the end of a word simultaneously, which are less common in English. Allophones, on the other hand, relate to phonetics and refer to the variations in pronunciation of a single phoneme rather than morphological structures. Thus, the term "affixes" is the most appropriate choice involving both prefixes and suffixes.