有大神 能帮我解答一下，这几道题的答案为什么是选那几项么？？

[jianke3320]

Examine these SQL statements and their output:
SQL> select name,value
2from v$parameter
3where name like 'undo%';
NAMEVALUE
-------------------- ----------------
undo_management AUTO
undo_tablespace UNDO
undo_retention 900
SQL> select contents,retention
2from dba_tablespaces
3where tablespace_name='UNDO';
CONTENTSRETENTION
-------------- --------------------
UNDOGUARANTEE
SQL> select blocks,autoextensible,maxblocks
2from dba_data_files
3Where tablespace_name='UNDO';
BLOCKS AUT MAXBLOCKS
------------- ----- ----------
6400NO 0
Which two are true?
A)Transactions will wait until free space becomes available in the undo tablespace when they havefailed to allocate space
B)The undo tablespace will grow automatically if there is not enough space to retain active undo
C)Inactive undo will be retain for at least 15 minutes
D)Expired undo will be retained as long as possible within the limits of the current size of the undo
tablespace
E)Active undo will be retained as long as needed by the transactions

Answer：CE




Examine these SQL statements and their output:
SQL> select name,value
2from v$parameter
3where name like 'undo%';
NAMEVALUE
-------------------- ----------------
undo_management AUTO
undo_tablespace UNDO
undo_retention 900
SQL> select contents,retention
2from dba_tablespaces
3where tablespace_name='UNDO';
CONTENTSRETENTION
-------------- --------------------
UNDONOGUARANTEE
SQL> select blocks,autoextensible,maxblocks
2from dba_data_files
3Where tablespace_name='UNDO';
BLOCKS AUT MAXBLOCKS
------------- ----- ----------
6400YES 64000
Which two are true?
A)Inactive UNDO will be retained as long as possible within the limits of the current size of the UNDO
tablespace.
B)The UNDO tablespace can grow automatically if there is not enough space to retain active UNDO.
C)Active UNDO will be retained as long as needed by transactions.
D)Inactive UNDO will never be retained for more than 15 minutes.
E)Inactive UNDO will always be retained for at least 15 minutes.

Answer：CE




Examine these SQL statements and their output:
SQL> select name,value
2from v$parameter
3where name like 'undo%';
NAMEVALUE
-------------------- ----------------
undo_management AUTO
undo_tablespace UNDO
undo_retention 900
SQL> select contents,retention
2from dba_tablespaces
3where tablespace_name='UNDO';
CONTENTSRETENTION
-------------- --------------------
UNDONOGUARANTEE
SQL> select blocks,autoextensible,maxblocks
2from dba_data_files
3Where tablespace_name='UNDO';
BLOCKS AUT MAXBLOCKS
------------- ----- ----------
6400YES 64000
Which two are true?
A)Inactive expired UNDO will be retained as long as possible within the limits of the current size of the UNDO tablespace.
B)The UNDO tablespace can grow automatically if there is not enough space to retain active UNDO.
C)Active UNDO will be retained as long as needed by transactions.
D)Inactive expired UNDO will never be retained for more than 15 minutes.
E)Inactive expired UNDO will always be retained for at least 15 minutes.

Answer：BC




Examine these SQL statements and their output:
SQL> select name,value
2from v$parameter
3where name like 'undo%';
NAMEVALUE
-------------------- ----------------
undo_management AUTO
undo_tablespace UNDO
undo_retention 900
SQL> select contents,retention
2from dba_tablespaces
3where tablespace_name='UNDO';
CONTENTSRETENTION
-------------- --------------------
UNDOGUARANTEE
SQL> select blocks,autoextensible,maxblocks
2from dba_data_files
3Where tablespace_name='UNDO';
BLOCKS AUT MAXBLOCKS
------------- ----- ----------
6400NO 0
Which three are true?
A)Active UNDO might be retained for 15 or more minutes.
B)Inactive UNDO might be retained for 15 or more minutes.
C)The UNDO tablespace is guaranteed to be retained for ever.
D)Expired UNDO might be retained for 15 or more minutes.
E)UNDO Blocks are retained for 900 days.
F)UNDO segments are guaranteed to be retained for ever.

Answer：ABD