adding another domain user as domain admins group

I am in a single forest, with multi-domain environment - domain A,B and C, is there a way to add a user or a group from domain B to domain C's domain admins group? It sounds that the domain admins group only accepts contacts or other objects and not users or groups if adding objects from another domain. And also domain admins group is a global group so cannot add a universal group either. So, can anyone please help me out?

What are you trying to do anyways? The priviledges held by members of Domain Admins are for the most part result from the fact that this group is by default a member of local Administrators group on all domain member computers and the domain local Administrators groups. You can try to add an arbitrary account from the domain B, such as a domain user or a domain global/universal group, to local Administrators group of designated computers in domain B, which can be fairly easily done using Restricted Groups GPO setting.

I dont know what you are try to do but you need to know which type of groups are visible from one domain to another domain. There are three types of groups, that is, Domain Local, Global and Universal. The domain local groups can include global groups and are usually the group type that has permissions assigned for it.

You can try to add these accounts to local Administrators groups, local domain and local groups on all domain member computers, in both domains.