List all the corresponding classes for attributes of image id 8.
classes for attributes refers to ATT_CLASS; image id 8 refers to IMG_ID = 8
SELECT T2.ATT_CLASS FROM IMG_OBJ_att AS T1 INNER JOIN ATT_CLASSES AS T2 ON T1.ATT_CLASS_ID = T2.ATT_CLASS_ID WHERE T1.IMG_ID = 8