Phonology investigates which of the following?

Phonology is the branch of linguistics that focuses on the systematic organization of sounds in languages. It examines how sounds function and interact within a particular language, making 'rules for pronunciation in a language' the core concern of phonology. This includes studying how different sounds may alter meaning when combined, as well as what sound patterns are permissible within a given language.

In contrast, studying individual phonetic sounds would align more closely with phonetics, which is about the physical properties of sounds themselves rather than their use in language systems. The creation of grammatical sentences pertains to syntax, which deals with how words combine to convey meaning, while the cultural implications of language fall under sociolinguistics or anthropology rather than phonological study. Thus, the focus on the rules that govern sound patterns in a language is what defines the study of phonology.