This is a transitive trust which is a two-way correlation routinely made among parent and child domains in a microsoft active directory forest and when a new domain is produced, it bonds resources with its parent domain by evasion in which allowing an valid user to access resources in together the child and parent.
XLS would be it, avi contains like sounds and stuff
I am not sure but I think that it is either the First option or the Third option but you would probably need more information.
