An affix is a word part added to the beginning or end of a word.
Affix is a term which includes prefixes (word parts added to the beginning of a word) and suffixes (word parts added to the end of a word). Affixes are used when you want to create a new word out of an old one. For example:
to imagine (verb) + -ation (suffix) = imagination (noun)
pre- (prefix) + determined (adjective) = predetermined (adjective)
A is incorrect because that is a homonym; B is incorrect because affixes include both the beginnings and endings of words; D is incorrect because that is a root.