Answer:
The best answer is C. Morphemes.
Explanation:
Morphemes are the smallest parts of speech which make sense, such as prepositions like "in", "of", or even prefixes like "de", "un", among others. When people are about to produce sentences they use their "mind data" to put morphemes together in order to produce phrases, words, clauses, sentences with different meanings and contexts. That is the reason for people to replace and/or mistake one phrase and/or morpheme here and there in their speech, because they may change sentence constructions or even word constructions at the real time building.