Once vCenter 4.x has been installed, a License Server is required in which of the
following instances?

A.
To support ESXi 4.x Hosts

B.
To support ESX 3.5 Hosts

C.
A License Server is no longer required

D.
A License Server is always required

Explanation:
vSphere uses a new centralized license reporting and management structure, which
means that if all ESX hosts are upgraded to version 4, no license server or host license
file is needed. ESX 3.5 hosts still require access to a license server, which can be used by
the vSphere Virtual Center by configuring the License Server option under
Administration-Server Settings.