Database: sing_contest (difficulty: simple)
Question: What are the voice sound quality score, rhythm tempo score and stage presence score performed by the participant named 'Iskren Petsov'?
SQL: SELECT T1.voice_sound_quality ,  T1.rhythm_tempo ,  T1.stage_presence FROM performance_score AS T1 JOIN participants AS T2 ON T1.participant_id  =  T2.id WHERE T2.name  =  'Iskren Petsov'