What is the title of the episode that has the highest number of crews in the Art Department?
the highest number of crews refers to max(count(person_id)); in the Art Department refers to category = 'Art Department'
SELECT T2.title FROM Credit AS T1 INNER JOIN Episode AS T2 ON T1.episode_id = T2.episode_id WHERE T1.category = 'Art Department' GROUP BY T2.episode_id ORDER BY COUNT(T1.category) DESC LIMIT 1