A. No. A DC can provide domain services for only one Active Directory (AD) domain. You can configure a DC as a Global Catalog (GC) server, which means the DC would also store a read-only copy of a subset of attributes for all domains in the forest, but the DC still couldn't provide authentication services for other domains in the forest.

A DC can also run AD Lightweight Directory Services (AD LDS)—previously known as AD Application Mode (ADAM)—partitions, but, again, these partitions aren't domains, they're LDAP-accessible directory services.