What is the name and country for the artist with most number of exhibitions?
SELECT T2.name , T2.country FROM exhibition AS T1 JOIN artist AS T2 ON T1.artist_id  =  T2.artist_id GROUP BY T1.artist_id ORDER BY count(*) DESC LIMIT 1
artist with most number of exhibitions refers to MAX(COUNT(exhibition)); name and country for the artist refers to artist.name, artist.country;