Answer:
Semantics
Step-by-step explanation:
In linguistics, syntax is the study of phrases and sentences. It also describes the set of rules of grammar that these sentences obey. It doesn't describe or govern the way meanings are assigned to morphemes - the smallest meaningful unit of a language.
Semantics on the other hand is the study of the meaning of sentences. It contains a system of rules governing how meanings are given to morphemes, phrases and sentences.
Phonology is a great branch in linguistics that deals with the study of speech sounds in languages.
Regularization is another branch in linguistics that observe languages in the bid to replace irregular forms in syntax, semantics and even morphology in that language with the regular forms.
Out of the described options, the one that has to do with meanings of morphemes is Semantics.