Following a successful migration，it is highly recommended that concurrent Volume Groups be Converted to enhanced concurrent capable Volume Groups.  In order to follow this recommendation，what step must be completed first？（）  

A、 The Volume Groups must be changed with chvg -E vgname.

B、 The Volume Groups must be a member of a resource group and must be varied on al nodes of       the cluster.

C、 The Volume Groups must be a member of a resource group and must be varied off all nodes      of the cluster.

D、 The Volume Grups cannot be changed to enhanced concurrent capable because they must be      recreated with mkvg -C vgname.