Which statement is true about the execution of the command?

B

I think it is C

16.9.6 DDL Statements on Tables Enabled for Flashback Data Archive
Flashback Data Archive supports only these DDL statements:

ALTER TABLE statement that does any of the following:

Adds, drops, renames, or modifies a column
Adds, drops, or renames a constraint
Drops or truncates a partition or subpartition operation
TRUNCATE TABLE statement

RENAME statement that renames a table

Flashback Data Archive does not support DDL statements that move, split, merge, or coalesce partitions or subpartitions, move tables, or convert LONG columns to LOB columns.

For example, the following DDL statements cause error ORA-55610 when used on a table enabled for Flashback Data Archive:

ALTER TABLE statement that includes an UPGRADE TABLE clause, with or without an INCLUDING DATA clause

ALTER TABLE statement that moves or exchanges a partition or subpartition operation

DROP TABLE statement

If you must use unsupported DDL statements on a table enabled for Flashback Data Archive, use the DBMS_FLASHBACK_ARCHIVE.DISASSOCIATE_FBA procedure to disassociate the base table from its Flashback Data Archive. To reassociate the Flashback Data Archive with the base table afterward, use the DBMS_FLASHBACK_ARCHIVE.REASSOCIATE_FBA procedure. Also, to drop a table enabled for Flashback Data Archive, you must first disable Flashback Data Archive on the table by using the ALTER TABLE … NO FLASHBACK ARCHIVE clause.

B
Remember that DDLs that alter the structure of a table (such as drop/modify column, move table, drop partition, truncate table/partition, and add constraint) invalidate any existing undo data for the table. If you try to retrieve data from a time before such a DDL executed, error ORA-01466 occurs. DDL operations that alter the storage attributes of a table (such as PCTFREE, INITRANS, and MAXTRANS) do not invalidate undo data.

I think its A

While flashback archiving is enabled for a table, some DDL statements are not allowed on it and will generate an ORA-55610 error. The following operations are disallowed:
ALTER TABLE statement that includes an UPGRADE TABLE clause, with or without an INCLUDING DATA clause
ALTER TABLE statement that moves or exchanges a partition or subpartition operation
DROP TABLE statement

The DBMS_FLASHBACK_ARCHIVE package provides a number of subprograms that extend the functionality of the Flashback Data Archive functionality of Oracle. One of the more common uses is to allow DDL changes to be made to a table that has had flashback archive enabled. Once Flashback Data Archive has been enabled for a table, users are prevented from issuing any DDL statements on it. The following example will disassociate the DEPT table from its history table:
EXEC DBMS_FLASHBACK_ARCHIVE.DISASSOCIATE_FBA(‘ HR’,’ DEPT’);
Once the above command has been executed, it is possible to make DDL changes to the DEPT table (for example adding a column) that would have generated an error because of the associated history table.
Once the DDL has been completed, the following command will reassociate the table with its history table:
EXEC DBMS_FLASHBACK_ARCHIVE.REASSOCIATE_FBA(‘ HR’,’ DEPT’);

Morris, Matthew (2015-06-01). Study Guide for 1Z0-067: Upgrade Oracle9i/10g/11g OCA to Oracle Database 12c OCP: Oracle Certification Prep (Kindle Locations 2895-2900). ODB Press. Kindle Edition.

C – tested:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 – 64bit Production
select sysdate from dual;
SYSDATE
——————-
2016-07-05 13:13:03
update scott.emp set sal=sal+100 where empno=7788;
commit;
select sal from scott.emp as of timestamp to_timestamp(‘2016-07-05 13:13:03′,’YYYY-MM-DD HH24:MI:SS’) where empno=7788;
SAL
————————————————–
3100
select sal from scott.emp where empno=7788;
SAL
————————————————–
3200

alter table scott.emp add phone number(12);
select sal from scott.emp as of timestamp to_timestamp(‘2016-07-05 13:13:03′,’YYYY-MM-DD HH24:MI:SS’) where empno=7788;
SAL
————————————————–
3100

And, here are some free 1Z0-067 dumps from Google Drive for referring: https://drive.google.com/open?id=0B-ob6L_QjGLpUDBvX3EwWkRJRnM

Good Luck!