[单选] You need to change the definition of an existing table. The COMMERCIALS table needs its DESCRIPTION column changed to hold varying length characters up to 2000 bytes. The column can currently hold 1000 bytes per value. The table contains 20000 rows. Which statement is valid?（）

变配电所常采用的电源引入方式为T接和（）接。 You have issued a SHUTDOWN ABORT command to bring down your database instance. Consider the stepsthat will be performed later when you open the database： 1. SGA is allocated. 2. Control file is read. 3. Redo log files are read. 4. Instance recovery is started. 5. Background processes are started. 6. Data files are checked for consistency. 7. Server parameter file or the initialization parameter file is read.  Which option has the correct order in which these steps occur（） 7， 1， 5， 2， 3， 6， 4。 1， 2， 3，7， 5， 6， 4。 7， 1， 4， 5， 2， 3， 6。 1， 7， 5， 4， 2， 3， 6。 参加新型农村社会养老保险的农村居民，符合国家规定条件的，按年领取新型农村社会养老保险待遇。 You work as a database administrator for Supportcenter.cn. You are using Recovery Manager （RMAN） to perform backups in your databases. Which four backup operations can be performed using RMAN？（） A backup of the target database when it is mounted。 A backup of online redo log files when the database is open。 A backup of only used data blocks in the file beingbeingbackup up。 A backup of online， read/write data files when the database is open。 A backup of only those data blocks that have changed since a previous backup。 A backup of online， read/write data files when the database is in the NOMOUNT state.。 微量元素 You need to change the definition of an existing table. The COMMERCIALS table needs its DESCRIPTION column changed to hold varying length characters up to 2000 bytes. The column can currently hold 1000 bytes per value. The table contains 20000 rows. Which statement is valid?（）