Explanation
A: Setting a PDB resource plan is optional. If not specified, all sessions within the PDB are treated equally.
* In a non-CDB database, workloads within a database are managed with resource plans.
In a PDB, workloads are also managed with resource plans, also called PDB resource plans.
The functionality is similar except for the following differences:
/ Non-CDB Database
Multi-level resource plans
Up to 32 consumer groups
Subplans
/ PDB Database
Single-level resource plans only
Up to 8 consumer groups
(not B) No subplans

*Flashback Database uses its own logging mechanism, creating flashback logs and storing them in the fast recovery area(C). You can only use Flashback Database if flashback logs are available. To take advantage of this feature, you must set up your database in advance to create flashback logs.
*To enable Flashback Database, you configure a fast recovery area and set a flashback retention target. This retention target specifies how far back you can rewind a database with Flashback Database.
From that time onwards, at regular intervals, the database copies images of each altered block in every data file into the flashback logs. These block images can later be reused to reconstruct the data file contents for any moment at which logs were captured.(F)
Incorrect: Not E:You cannot use Flashback Database alone to retrieve a dropped data file. If you flash back a database to a time when a dropped data file existed in the database, only the data file entry is added to the control file. You can only recover the dropped data file by using RMAN to fully restore and recover the data file.
Reference: OracleDatabase Backup and Recovery User's Guide12c R

*SET_TABLE_PREFS Procedure
This procedure is used to set the statistics preferences of the specified table in the specified schema.
*Example:
Using Pending Statistics
Assume many modifications have been made to the employees table since the last time statistics were gathered. To ensure that the cost-based optimizer is still picking the best plan, statistics should be gathered once again; however, the user is concerned that new statistics will cause the optimizer to choose bad plans when the current ones are acceptable. The user can do the following:
EXEC DBMS_STATS.SET_TABLE_PREFS('hr', 'employees', 'PUBLISH', 'false'); By setting the employees tables publish preference to FALSE, any statistics gather from now on will not be automatically published. The newly gathered statistics will be marked as pending.

C: During the first execution of a SQL statement, an execution plan is generated as usual.
D: if multi-column statistics are not present for the relevant combination of columns, the optimizer can fall back on cardinality feedback.
(not B)* Cardinality feedback. This feature, enabled by default in 11.2, is intended to improve plans for repeated executions.
optimizer_dynamic_sampling
optimizer_features_enable
* dynamic sampling or multi-column statistics allow the optimizer to more accurately estimate selectivity of conjunctive predicates.
Note:
* OPTIMIZER_DYNAMIC_SAMPLING controls the level of dynamic sampling performed by the optimizer.
Range of values. 0 to 10
* Cardinality feedback was introduced in Oracle Database 11gR2. The purpose of this feature is to automatically improve plans for queries that are executed repeatedly, for which the optimizer does not estimate cardinalities in the plan properly. The optimizer may misestimate cardinalities for a variety of reasons, such as missing or inaccurate statistics, or complex predicates. Whatever the reason for the misestimate, cardinality feedback may be able to help.