Please list the occupations of the customers over 40 and have sent a true response to the incentive mailing sent by the marketing department.
over 40 refers to age > 40; RESPONSE = 'true';
SELECT DISTINCT T1.OCCUPATION FROM Customers AS T1 INNER JOIN Mailings1_2 AS T2 ON T1.ID = T2.REFID WHERE T1.age > 40 AND T2.RESPONSE = 'true'