* In most cases, ADDM output should be the first place that a DBA looks when notified of a performance problem.
* Performance degradation of the database occurs when your database was performing optimally in the past, such as 6 months ago, but has gradually degraded to a point where it becomes noticeable to the users. The Automatic Workload Repository (AWR) Compare Periods report enables you to compare database performance between two periods of time.
While an AWR report shows AWR data between two snapshots (or two points in time), the AWR Compare Periods report shows the difference between two periods (or two AWR reports with a total of four snapshots). Using the AWR Compare Periods report helps you to identify detailed performance attributes and configuration settings that differ between two time periods.
Reference: Resolving Performance Degradation Over Time

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

About Startup Dependencies
Oracle Restart ensures that Oracle components are started in the proper order, in accordance with component dependencies. For example, if database files are stored in Oracle ASM disk groups, then before starting the database instance, Oracle Restart ensures that the Oracle ASM instance is started and the required disk groups are mounted. Likewise, if a component must be shut down, Oracle Restart ensures that dependent components are cleanly shut down first.
Oracle Restart also manages the weak dependency between database instances and the Oracle Net listener (the listener): When a database instance is started, Oracle Restart attempts to start the listener. If the listener startup fails, then the database is still started. If the listener later fails, Oracle Restart does not shut down and restart any database instances.
http://docs.oracle.com/cd/E16655_01/server.121/e17636/restart.htm#ADMIN12710

B: SYSDG administrative privilege has ability to perform Data Guard operations (including startup and shutdown) using Data Guard Broker or dgmgrl.
D: SYSASM
The new (introduced in 11g) SYSASM role to manage the ASM instance, variable extent sizes to reduce shared pool usage, and the ability of an instance to read from a specific disk of a diskgroup E (Not A): SYSDBA is like a role in the sense that it is granted, but SYSDBA is a special built-in privilege to allow the DBA full control over the database Incorrect:
Not C: SYSKM. SYSKM administrative privilege has ability to perform transparent data encryption wallet operations.
Note:
Use the V$PWFILE_USERS view to see the users who have been granted administrative privileges.

Explanation/Reference: https://blogs.oracle.com/oraclemagazine/unify-auditing