Which two circumstances would prevent the option of joining a Linked Mode group during vCenter Serve

Which two circumstances would prevent 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 a VirtualCenter Server installation.