An ESX Host gains exclusive access to Virtual Machines created on NFS datastores using?

A.
Distributed File Locking

B.
NFS File Locking Protocol

C.
SCSI Reservations

D.
a special .lck-XXX lock file

Explanation:
ESX ESX Configuration Guide ESX 4.0 vCenter Server 4.0 When your host accesses a virtual machine disk file on an NFS-based datastore, a .lck-XXX lock file is generated in the same directory where the disk file resides to prevent other hosts from accessing this virtual disk file. Do not remove the .lck-XXX lock file, because without it, the running virtual machine cannot access its virtual disk file.