Question: Who among the actors starred in a NC-17 rated film? Provide only the last name of the actors.
SQL: SELECT T1.last_name FROM actor AS T1 INNER JOIN film_actor AS T2 ON T1.actor_id = T2.actor_id INNER JOIN film AS T3 ON T2.film_id = T3.film_id WHERE T3.rating = 'NC-17'