What aspect of language does morphology relate to?

Morphology is a branch of linguistics that focuses on the structure and formation of words. It studies how words are constructed from smaller units known as morphemes, which are the smallest grammatical units in a language. These morphemes can be root words, prefixes, or suffixes, and by combining them, different words can be formed. Understanding morphology is essential for recognizing how words can change based on tense, plurality, and other grammatical aspects.

For instance, the word "unhappiness" consists of the prefix "un-", the root "happy," and the suffix "-ness." Morphology helps to explain how these parts combine to create a word with a specific meaning. Thus, the emphasis on the formation of words directly links morphology to its true focus, making it the correct answer in this context.