What is causing the Desktop OS machines to be reported as ‘Unregistered’?

Scenario: A Citrix Engineer found that a high number of Desktop OS machines are reported as

‘Unregistered’. The engineer successfully logs in to one of the affected Desktop OS machines as a domain user and finds that all of the affected Desktop OS machines are on the same hosting infrastructure.

Several Desktop OS machines on the same hosting infrastructure registered successfully.

However, the users in the environment have NOT reported any issues.

What is causing the Desktop OS machines to be reported as ‘Unregistered’?
A . The difference in the system date and time settings on the Desktop OS machines and the Delivery
Controller is greater than 5 minutes.
B . The computer account of the master image has been deleted from Active Directory.
C . The Broker Service is NOT running on the Delivery Controllers.
D . The Citrix License Server is NOT communicating over port 27000.

Answer: A