💡 Detailed Explanation
The prefix '非' (hi) means 'non-', 'un-', or 'anti-'. It is used to negate the word it attaches to, creating an opposite meaning. '非公式' (hikōshiki) means 'unofficial'. The other options are also negative prefixes but are used in different contexts. '不' (fu) often implies a lack or inability (e.g., 不可能 - impossible). '無' (mu) implies a complete absence (e.g., 無関係 - unrelated). '未' (mi) means 'not yet' (e.g., 未完成 - unfinished).