You are maintaining your database in Oracle10g. You perform a full user-managed backup every Sunday at 8：00 P.M. Your database is running in ARCHIVELOG mode. On Monday， at 9：00 A.M.， a tablespace is dropped. You decide to perform incomplete recovery to recover the dropped tablespace.  Which two clauses can you use with the RECOVER command？（）

In which situation will you run the script containing the following statement？（）  
CREATE CONTROLFILE REUSE DATABASE SALES NORESETLOGS ARCHIVELOG       
MAXLOGFILES 20       
MAXLOGMEMBERS 3       
MAXDATAFILES 30       
MAXINSTANCES 10       
MAXLOGHISTORY 1200       
LOGFILE       
GROUP 1 （  
’/disk1/prod/orders/db/log1a.dbf’，       
’/disk2/prod/orders/db/log1b.dbf’       
）SIZE 100K      
 GROUP 2 （  
’/disk1/prod/orders/db/log2a.dbf’，       
’/disk2/prod/orders/db/log2b.dbf’       
） SIZE 100K，       
DATAFILE  
’/disk1/prod/orders/db/database1.dbf’，                                          
’/disk2/prod/orders/db/file1.dbf ’；  

You are the Database Administrator （DBA） of your company. You execute the following statement on an Oracle 10g instance：  
SQL> ALTER SYSTEM SWITCH LOGFILE；  
Which two tasks are performed when the statement is executed？ （）

You are maintaining the SALES database of TeleStar Corporation. The online redo log configuration of the database is as follows：  

One of the redo log members， redo3b， is lost due to disk failure.   How will you recover the redo log member redo3b？（）