In Windows Server, which of the following is NOT a domain-level Flexible Single Master Operation (FSMO) role?

In Windows Server, which of the following is NOT a domain-level Flexible Single Master Operation (FSMO) role?

• Domain Naming Master
• Relative ID (RID) Master
• Infrastructure Master
• Primary Domain Controller (PDC) Emulator 

EXPLANATION

There are five FSMO Roles represented in a typical Windows Active Directory, three domain-level, two enterprise-level. The forest/enterprise level roles are Schema Master and Domain Naming Master. The domain roles are PDC Emulator, Infrastructure Master, and RID Master.
A more detailed breakdown of FSMO roles can be found here.