What encompasses the sound structure and system of a language?

The correct answer, which is phonology, refers specifically to the sound structure and system of a language. Phonology examines how sounds function and are organized within a particular language, including the rules that govern sound combinations and patterns. This encompasses elements such as phonemes (the smallest units of sound that can distinguish meaning) and syllable structure.

In contrast, grammar pertains to the rules and structures governing how words combine to form sentences, while semantics deals with the meaning of words and phrases in context. Phonetics, on the other hand, focuses on the physical production and perception of speech sounds rather than their role and function within a particular language system. Hence, phonology is the appropriate choice when discussing the overarching sound structure and system of a language.