What is the term for the word part placed before a word to change its meaning?

A prefix is a word part added before a root word to modify its meaning. It is commonly used in the English language to create new words. For example, in the word 'unhappy,' 'un-' is the prefix that changes the meaning of 'happy' to indicate the opposite. Suffixes, on the other hand, are word parts added at the end of a root word. Affix is a general term that includes both prefixes and suffixes. 'Vocab' is not a term related to word parts but rather refers to vocabulary. Therefore, the correct answer is A: Prefix.