Write SQL query to solve given problem: What are the attributes of the widest object in image 400?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T1.ATT_CLASS FROM ATT_CLASSES AS T1 INNER JOIN IMG_OBJ_ATT AS T2 ON T1.ATT_CLASS_ID = T2.ATT_CLASS_ID INNER JOIN IMG_OBJ AS T3 ON T2.IMG_ID = T3.IMG_ID WHERE T2.IMG_ID = 400 ORDER BY T3.W DESC LIMIT 1