Which option could be used for vSphere HA heartbeats?

A.
iSCSI LUN backing an RDM connected over 10GB Ethernet

B.
NFS datastore shared with the all hosts, sync, no_root_squash and read only options

C.
iSCSI LUN used for booting the master ESXi host

D.
FCP LUN on an 8GB active/active array backing a VMFS5 datastore