💡 Detailed Explanation
Translation of sentence: At lunchtime, we ate a delicious bento on top of the mountain.
- Grammatical point: Adjective modifying a noun directly.
- Explanation: To modify the noun お弁当 (bento) directly with the i-adjective おいしい (delicious), keep it in its dictionary/attributive form: 'おいしい お弁当'.
- Other choices are incorrect inflections for direct noun modification.