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

Answer: To support ESX 3.5 Hosts

Explanation:

The new centralized license key management introduces administration of licenses as a native feature starting with VMware vCenter 4, and no separate license server is required to manage and monitor the software. However, even though ESX 3.5 hosts can be managed by vCenter 4.x, they still require a VMware Infrastructure 3.5 license server