Which statements are true about graceful Routing Engines switchover (GRES)?

A.
Configuration on both Routing Engines must be synchronized.

B.
The backup Routing Engine cannot be managed through IP address because RPD does not run on backup the Routing Engine.

C.
Different hostnames must be configured on both Routing-Engines.

D.
Both Routing-Engines are managed through a single out-of-band-management IP address.

Explanation:
Enabling Graceful Routing Engine Switchover

By default, graceful Routing Engine switchover is disabled.
To configure graceful Routing Engine switchover, include the graceful-switchover statement at the [edit chassis redundancy] hierarchy level.

[edit chassis redundancy]

graceful-switchover;

When you enable graceful Routing Engine switchover, the command-line interface (CLI) indicates which Routing Engine you are using. For example:

{master} [edit]

user@host#

To disable graceful Routing Engine switchover, delete the graceful-switchover statement from the [edit chassis redundancy] hierarchy level.

Synchronizing the Routing Engine Configuration

Note: A newly inserted backup Routing Engine automatically synchronizes its configuration with the master Routing Engine configuration.
When you configure graceful Routing Engine switchover, you can bring the backup Routing Engine online after the master Routing Engine is already running. There is no requirement to start the two Routing Engines simultaneously.

Synchronizing Routing Engines

If your router has two Routing Engines, you can manually direct one Routing Engine to synchronize its configuration with the other by issuing the commit synchronize command. The Routing Engine on which you execute this command (requesting Routing Engine) copies and loads its candidate configuration to the other (responding Routing Engine). Both Routing Engines then perform a syntax check on the candidate configuration file being committed. If no errors are found, the configuration is activated and becomes the current operational configuration on both Routing Engines.

The commit synchronize command does not work if the responding Routing Engine has uncommitted configuration changes. However, you can enforce commit synchronization on the Routing Engines by using the force option. When you issue the commit synchronize command with the force option from one Routing Engine, the configuration sessions on the other Routing Engine will be terminated and its configuration synchronized with that on the Routing Engine from which you issued the command.