Which of the following circumstances prevents the option of joining a linked mode group during
vCenter Server installation (Choose Two)?

A.
An administrator is installing the first of the vCenter Server instances

B.
An administrator installed vCenter Server instances using different domain accounts

C.
An administrator has vCenter Server instances in multiple domains

D.
An administrator is upgrading an existing VirtualCenter Server installation

Explanation:
The following requirements apply to each vCenter Server system that is a member of a Linked Mode group:

DNS must be operational for Linked Mode replication to work.

The vCenter Server instances in a Linked Mode group can be in different domains if the domains have a two-way trust relationship. Each domain must trust the other domains on which vCenter Server instances are installed.

When adding a vCenter Server instance to a Linked Mode group, the installer must be run by a domain user who is an administrator on both the machine where vCenter Server is installed and the target machine of the Linked Mode group.

All vCenter Server instances must have network time synchronization. The vCenter Server installer validates that the machine clocks are not more than 5 minutes apart.