Question

homophones are words that
have exactly the same meaning
have completely opposite meanings
sound the same but have different meanings
are spelled the same but are pronounced differently

Explanation:

Homophones are defined as words that share the same pronunciation (sound the same) but have distinct meanings (and may have different spellings). The first option is synonyms, the second is antonyms, and the fourth is homographs (words spelled the same but pronounced differently). So the correct description for homophones is "sound the same but have different meanings".

Answer:

sound the same but have different meanings