Answer:
The correct answer is MORPHOLOGY.
Explanation:
Morphology is the branch of linguistics that studies the structure within words. Generally, a word can be divided into three parts: the prefix, the root, and the suffix. Each part adds meaning to the root or changes the category of the word.
For example, in the linguistic unit unhappiness we have the prefix "un" meaning "no", the root "happy", and the suffix "ness". In addition, the suffix "ness" turns the adjective "unhappy" into the abstract noun "unhappiness".
