Which two statements are true about nonstop bridging (NSB)?

Which two statements are true about nonstop bridging (NSB)? (Choose two.)

A.
NSB does not require all participating Routing Engines to run the same version of the Junos OS.

B.
NSB can be enabled under the protocols layer2-control hierarchy.

C.
NSB requires you to configure graceful Routing Engine switchover (GRES).

D.
NSB does not require you to configure graceful Routing Engine switchover (GRES).