Which two VMware software components can be updated by Update Manager?

Which two VMware software components can be updated by Update Manager? (Choose two.)

A.
ESX 3.5

B.
Virtual Appliances

C.
vCenter Server

D.
Guest OS

Explanation:
http://www.vmware.com/support/vsphere5/doc/vsphere-update-manager-51-releasenotes.html