💡 Detailed Explanation
The correct choice is '見つかりました' (was found / came to light) which is the past polite form of the intransitive verb '見つかる'. Because the particle before '鍵' is 'が' (subject marker), the intransitive verb is required. Sentence translation: 'The key I was searching for was found under the bed.' If the particle were 'を' (object marker), the transitive verb '見つけました' (found) would be correct. '見えました' means was visible, and '見せました' means showed.