A Customer Reports That Several VMs Have Become Unreachable or Invalid

A customer reports that several VMs have become Unreachable or Invalid in vCenter. What would you check or try first to solve this problem?

A) From the Host, stop and start the monitoring agent.
B) On the Host, from vCenter, try to re-scan the Datastores.
C) Place the host in maintenance mode.
D) Shut the host down and restart it.