John, a VMware Administrator, Has Set a Virtual Machine as Fault

John, a VMware administrator, has set a virtual machine as fault tolerant using VMware Fault Tolerance. The fault-tolerant pair of virtual machines has been working as expected for several weeks, but John is now receiving errors relating to the fault-tolerant pair. What is a likely cause of these error messages?

A) The hosts are at the same patch level.
B) There are only four identical hosts in the vSphere cluster.
C) The virtual machines only have one vCPU.
D) There is increased bandwidth on the physical network.