Question: Which film is rented for the most times by the customers? Please give its title.
SQL: SELECT T.title FROM ( SELECT T1.title, COUNT(T3.rental_id) AS num FROM film AS T1 INNER JOIN inventory AS T2 ON T1.film_id = T2.film_id INNER JOIN rental AS T3 ON T2.inventory_id = T3.inventory_id GROUP BY T1.title ) AS T ORDER BY T.num DESC LIMIT 1