Question: What attributes are used to describe the wall on image no. 27.
SQL: SELECT T4.ATT_CLASS FROM IMG_OBJ AS T1 INNER JOIN OBJ_CLASSES AS T2 ON T1.OBJ_CLASS_ID = T2.OBJ_CLASS_ID INNER JOIN IMG_OBJ_ATT AS T3 ON T1.IMG_ID = T3.IMG_ID INNER JOIN ATT_CLASSES AS T4 ON T3.ATT_CLASS_ID = T4.ATT_CLASS_ID WHERE T2.OBJ_CLASS = 'wall' AND T1.IMG_ID = 27 GROUP BY T4.ATT_CLASS