Which two circumstances might cause a DRS cluster to become invalid? (Choose two.)

A.
DRS has been disabled on one or more ESXi hosts.

B.
An ESXi host has been removed from the cluster.

C.
A migration on a virtual machine is attempted while the virtual machine is failing over.

D.
Virtual machines have been powered on from a vSphere Client connected directly to an ESXi
host.

Explanation:
http://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.vsphere.resmgmt.doc%2FGUID-C7417CAA-BD38-41D0-9529-9E7A5898BB12.html