Which two steps must be performed to carry out a unified ISSU on an EX Series Virtual Chassis?
(Choose two.)

A.
Enable GRES and NSR, then verify that the Routing Engines are synchronized.

B.
Download the new software package and copy it to both Routing Engines before the upgrade.

C.
Verify that the master and backup Routing Engines are running the same software version.

D.
Shut down the backup Routing Engine before the upgrade.