to minimize downtime, what is the Brocade recommended approach to fabric node upgrades?

A.
Upgrade the spine RBridges then the leaf RBridges.
B.
Upgrade the odd RBridges then the even RBridges.
C.
Upgrade the core RBridges then the edge RBridges.
D.
Upgrade the leaf RBridges then the spine RBridges.