Question

the primary purpose of a prefix is...
examples:
sagacious --> unsagacious
appropriate --> inappropriate
floor --> sub-floor

determine a words part of speech
establish a words denotation
the affixes attach to it
create an antonym

Explanation:

Looking at the examples: "un-" changes "sagacious" to its opposite "unsagacious", "in-" changes "appropriate" to "inappropriate", and "sub-" modifies "floor" to create a related term "sub-floor". These show prefixes attach to base words to modify or create new terms, which aligns with the option about affixes attaching. The other options are incorrect: prefixes don't determine part of speech alone, don't establish a word's core denotation, and not all prefixes create antonyms (like "sub-" here doesn't).

Answer:

the affixes attach to it