单项选择题 You have many users complaining about slow inserts into a large table. While investigating the reason， you find that the number of indexes on the table is high. You want to find out which indexes are not being used.  Which method would you follow to achieve this？（）

多项选择题 Users in your production database complain that they are getting the following error message while trying to insert rows into the ORDERS table：  ERROR at line 1：  ORA­01654： unable to extend index USERS.ORDERS_IND by 8 in tablespace INDEXES  While investigating， you find that the INDEXES tablespace has run out of space and there is no more free space on the disk where the data files are available.  Which two actions could you perform to overcome this error without affecting the queries that are currently being executed？（）

单项选择题 In one of your online transaction processing （OLTP） applications， most users frequently modify the values， including the key values， of the application tables. Some users generate application reports by using multiple application tables.  What is the best table structure that you can use to gain optimal performance？（）