What does it indicate when a cluster state is “Active attention”?

A.
The cluster member is booting: ClusterXL is running, but VPN-1/ NGX is not yet ready.

B.
Both cluster members are up and ready.

C.
Cluster members are running different versions: The newer version member is in the
readystate, while the older version member is in the active state.

D.
Traffic is being passed, but a problem has been detected: There are no other active members
in the cluster.